List of Special Elevator Modes

https://elevation.fandom.com/wiki/List_of_elevator_special_modes

by altrus • 5 years ago

326 206 5 years ago

elevation.fandom.com

mmazing• 5 years ago

I recall hearing of a mode one time where elevators would only go to the 2nd floor and not the 1st. Something for crime, etc.

Maybe it was from a movie or something ...

Edit : Thanks! Found it - https://en.wikipedia.org/wiki/Elevator#Riot_mode

rail• 5 years ago

Riot mode.

dkdbejwi383• 5 years ago

So only going 0 to 2 and that’s it? Not sure I understand the use case.

Akronymus• 5 years ago

1st floor, for many people, refers to the ground floor.

Basically, it excludes the ground level/publicly accessible floor, like a hotel lobby.

royjacobs• 5 years ago

If you're interested in elevators and the hacking thereof I would also highly recommend this talk: https://youtu.be/ZUvGfuLlZus

simlevesque• 5 years ago

The kind of videos you can watch once a year. Deviant Ollam is so interesting.

phnofive• 5 years ago

Pet mode is interesting; it allows you to take your pet on an express ride to your desired floor at the cost of a slightly slower speed.

Aardwolf• 5 years ago

Or can be abused, without pet, to go directly to your desired floor without being interrupted by those passengers at other floors.

pjerem• 5 years ago

In Japan, where this pet mode exists, honor and respect of social rules are something, and I doubt you would take the risk to be seen leaving an elevator in pet mode without a pet.

dbcurtis3• 5 years ago

Some destination-dispatch systems used in high-end residential towers will not schedule pet owners and non-pet owners to the same cab at the same time. Which makes a lot of sense.

dmurray2• 5 years ago

I'd expect it to be more of a problem having multiple pet owners in the same car.

Y_Y• 5 years ago

Pros
Does not infect other passengers if the animal has an infection

I'm glad that elevators are concerned about such a scenario.

hawk_2• 5 years ago

my personal favorite is the Sabbath mode https://elevation.fandom.com/wiki/Sabbath_service_(SHO)

not to pick on a specific belief system, but it's quite interesting the lengths people go to follow the letter but not the spirit of things.

chimeracoder• 5 years ago

not to pick on a specific belief system, but it's quite interesting the lengths people go to follow the letter but not the spirit of things.

That's not the way observant Jewish people look at it at all. You're assuming that these workarounds are not "following the spirit", but according to them, the workarounds are as much a part of the spirit of the law as the law itself.

tamaharbor• 5 years ago

Tell that to your nearest Eruv.

AndrewDucker• 5 years ago

The letter was, they believe, the word of God. If God hadn't meant the loophole to be there then he would have used different words. The loophole is divine.

krapp5• 5 years ago

If God hadn't meant the loophole to be there then he would have used different words. The loophole is divine.

One could just as well state that if God had meant the loophole to be there, he would have mentioned it.

LudwigNagasena2• 5 years ago

If the loophole seems to go directly against intended meaning, can you say it’s there?

michaelhoffman• 5 years ago

The prohibition is on doing work generally, with a specific prohibition on kindling a fire, which was quite a lot of work millennia ago.

Does using a device that allows you to avoid walking up many flights of stairs really violate the spirit of a law prohibiting work on the sabbath?

moduspol• 5 years ago

And for that matter, where is the line drawn?

The other workaround I had heard for this is to have a non-Jew hired specifically to stand in the elevator and push buttons on behalf of Jews on the sabbath. But they'd still have to speak the floor so the attendant would know what button to push, right?

If so, what if an elevator had basic voice recognition? Speaking the floor number to a machine is no more work than speaking it to an attendant, right?

Maybe this rule interpretation was originally made back when elevators generally had attendants and did require some expertise to operate (e.g. to stop at the right spots)? And then didn't get rolled back when it became essentially trivial?

hawk_2• 5 years ago

if the idea is to not work then pressing a button isn't going to change anything. if the elevator is being taken to do some work, again pressing the button has nothing to do with it.

ars6• 5 years ago

"Work" is a bad translation. A better translation would be "creative activity". Fire is a problem not because it's work to light, but because you are creating heat from wood.

LegitShady• 5 years ago

https://en.wikipedia.org/wiki/39_Melachot

It’s not quite as you say. There are more specifics involved than just ‘work generally or kindling a fire’ - but few people except religious Jews would care about the details.

jackbeck4• 5 years ago

There are sects (like the ultra orthodox) who don't use Sabbath mode specifically for this reason. They say that the added weight causes the elevator's motor to work harder thereby desecrating the Sabbath.

dmurray2• 5 years ago

Are they allowed to go down?

Also, depending on the counterweight and the current load of the elevator, adding an extra person to it might tax the motor less even when ascending.

chadash3• 5 years ago

In Orthodox Judaism, the letter of the law typically is the spirit of the law. Not a perfect analogy, but think of the talmud as similar to the tax code. There are things that are black, things that are white and things that are gray. If the tax code said there's a 5% sales tax on tangerines, clementines, navel oranges, lemons, and grapefruit, I'm probably not gonna volunteer to pay taxes on my Sumo Citruses, because it's not explicitly in there. Perhaps doing so would be in the spirit of the law, but that's just not the way people think when it comes to taxes. Same thing in Judaism... if it's technically legal, you can do it (this stems from the notion that the Jewish legal rules are of divine origin, and so if something was excluded, then its absence is intentional)[1].

Of course, much like the tax code, there are gray areas where different accountants (rabbis) may interpret the rules differently. One place where the analogy diverges is that in Judaism, there are lots of areas where the earlier generations of rabbis acknowledge something to be technically allowed according to the divine rules, but they forbid it anyway, either because they felt there was some societal benefit to doing so, or because they felt that adding an additional prohibition would prevent people from accidentally breaking the divine rule [1].

[1] Of course, the analogy breaks down, because it's more complicated than this. There are plenty of areas where people are customarily stricter, even if something is ok by the letter of the law. This applies to Sabbath Mode on elevators, which many Orthodox Jews won't use, but won't necessarily say that it's prohibited.

[2] An example of this is the prohibition of eating milk and meat in the same dish. Technically, the divine rule is no cooking milk and meat together, but the rabbis added an extra rule of no eating them together to make sure that people wouldn't come to cook them together.

asciimov2• 5 years ago

So my Jewish friends could technically eat a cheese burger, as long as the cheese was placed on the burger after cooking?

Would they have to wait till the burger cools down so that it doesn't melt the cheese? (Here I am concerned about carryover heating/cooking being considered cooking by law.)

I am endlessly fascinated by religious laws and their implications/consequences.

LudwigNagasena2• 5 years ago

First, when people feel that the tax code doesn’t represent the spirit of the law, they change the wording, likely they will amend it and put the same tax on Sumo Citruses as on other citruses. So the tax code and the Talmud are quite different animals.

Second, I am pretty sure the Talmud is not so precise to the point of specifically mentioning pressing pressing buttons on an elevator. So the analogy kind of doesn’t work there again.

derefr3• 5 years ago

this stems from the notion that the Jewish legal rules are of divine origin, and so if something was excluded, then its absence is intentional

I would like to understand the reasoning behind the belief that even legal rules of divine origin would include mention of things human culture would have had no concept of, and human language no word for, in the time the rule was made — such that the rules would be "complete for all future time" rather than "those relevant as of the time of covenant."

Wouldn't even a god think it more optimal to hold off on telling us rules about e.g. which synthetic meats are kosher, until we invent such things?

It seems awfully suspicious to the validity of that interpretation, that there are plenty of specific/concrete prohibitions given amongst divine rulings, but of those, none are about things that were entirely mysterious at the time, written down "as spoken" without understanding, only able to be made sense of centuries/millennia later.

In fact — the Hebrew god is an intercessor god, not an absent god; don't they already "amend" their own previous rules whenever they communicate specific orders / demands / requirements to particular people? Does that not, by itself, disrupt the interpretation of the initial set of laws given being a perfect closed set, never to be updated, applicable to all future circumstances? Would a perfect body of divine law not already imply those orders / demands / requirements, such that there would be no need for further communication?

1-more• 5 years ago

acknowledge something to be technically allowed according to the divine rules, but they forbid it anyway, either because they felt there was some societal benefit to doing so, or because they felt that adding an additional prohibition would prevent people from accidentally breaking the divine rule

There are of also cases where a societal benefit outweighed new knowledge about biology. Spontaneous generation meant that it's ok to kill lice on the Sabbath and eat fish with worms in it (which nearly all fish do) so long as the worms are of the kind that hatch within the fish. Well lice don't spontaneously generate and the worm in question lives outside the fish, but are you really gonna tell people to not kill lice any day of the week and totally get rid of part of their diet? It's a fun bit of tradition I think.

https://www.kashrut.com/articles/WormsInFish/

int_19h2• 5 years ago

The analogy breaks down even for this very example, because the reason why you're not supposed to use the elevator buttons is because operating some electric device is considered a form of "kindling a fire", which is prohibited on Sabbath - which is definitely not a literal interpretation of the corresponding scriptural prohibition.

jackbeck4• 5 years ago

Previous discussion here: https://news.ycombinator.com/item?id=27010617

canadianfella• 5 years ago

Can we all agree that religion is pretty silly?

grayhatter• 5 years ago

It seems not on HN you can't.

disruptthelaw• 5 years ago

I took my gap year in israel with a religious Jewish friends. We were slight stoners back then and on sabbath in order for him to get high I’d have to light a bong in a cupboard and fill the cupboard with smoke and then swap places with him. This was multiple times per sabbath every sabbath. I also had to constantly open the fridge for him because of the automatic light. I found these rituals ridiculous (20 years later I still do) and we fought over it and decided to part ways for the rest of the gap year.

ars6• 5 years ago

He should not have done that. In general a Jew is not permitted to ask a non-Jew to do things that are forbidden to him.

Some exceptions are things necessary for normal life, that would be impossible to do in advance. A classic example is lighting a fire for heating (back when that was done with a pile of wood), and minor medical needs. (Major medical needs the Jew would violate the Shabbath and do himself.)

Getting high is not a necessity, and the fridge switch could have been taped before the Shabbath.

908B64B197• 5 years ago

You'll enjoy this then (when Richard Feynman encountered something similar):

https://www.reddit.com/r/atheism/comments/ev3gy/excerpt_from...

el_nahual• 5 years ago

There are a few sibling comments explain this by saying that, since the law is divine, so are the loopholes. That doesn't tell the whole story.

A big chunk of judaism has always centered about cultural preservation. In a way, the careful crafting of ridiculous loopholes is a stronger indicator about caring that the law exists --ie, presereving the culture-- than blindly following it. And so it's allowed and celebrated.

("What happens when a culture that is built on the notion of being an opressed people finds itself in a position of dominance" is an interesting question and left as an exercise to the reader.)

thrdbndndn2• 5 years ago

With all respect, what you said makes zero sense to me.

I don't see how "caring that the law exists" equals to "preserving the culture" (at least not see it in a good way), or how it's not "blindly following it".

seigando3• 5 years ago

What qualifies you to know the spirit and letter better than those that adhere to and study this belief system?

wolverine8762• 5 years ago

s quite interesting the lengths people go to follow the letter but not the spirit of things.

Perhaps it appears that way to you, but what do you know about the 'spirit' of Jewish law compared to generations of life-long practitioners and rabbis?

DonHopkins8• 5 years ago

As if they were so clever they could trick God. Pretty presumptuous and irreverent. Why worship a God you believe is such a gullible chump?

sevrinsky2• 5 years ago

Shabbat observance is a massive world unto itself. It originates in Biblical sources (i.e. "the word of God"), but has developed throughout the entire rabbinic tradition, from the time of the prophets through the Talumdic era, and subsequently to the modern day.

Today, it is universally accepted in Orthodox Judaism that direct active interaction with electrical appliances is forbidden on Shabbat. However, one may benefit from and "use" devices and automated systems set in place before Shabbat, including light timers, fridges, and heating plates.

To be clear: nobody is "tricking" God by using a Shabbat elevator. Rather, this maintains the special nature of the day within the parameters established by centuries of tradition and scholarship ultimately based on God's commandments, while facilitating navigating our modern world.

Animats2• 5 years ago

Oh, the workarounds. See KosherSwitch.[1]

[1] http://www.kosherswitch.com

dinkleberg2• 5 years ago

Maybe this is common knowledge, but I never knew people used fandom for topics like this. I’m amazed that it had 800+ articles and over 1000 videos on a wiki dedicated to elevators.

fortran77• 5 years ago

There are many "elevator spotters" on YouTube. I can watch elevator videos for hours.

For example: https://www.youtube.com/watch?v=nE9x-S_3sdY

It's a very interesting community:

See: https://www.youtube.com/watch?v=iz9ZzIgyDR8

jdmichal2• 5 years ago

I remember seeing an elevator once that lit up both the up and down arrows when arriving if it didn't have a set destination yet. I called it Schroedinger's elevator -- neither going up or down until observed to move.

dinkleberg2• 5 years ago

I love this aspect of HN. I never would’ve known there was a community around a shared interest in elevators, yet this topic has hit the top of HN and a bunch of members of that community have all gathered here.

thrdbndndn2• 5 years ago

I think the surprising part (to me at least) isn't there are communities for elevator lovers, but there is a wiki about it on Fandom.

ethbr0• 5 years ago

Seems as good a place as any to OT, but does anyone know of a vacuum tube wiki?

I may have acquired some Otis elevator power(?) tubes, but have no idea where to go for part schematics or identification. I'd love to build them into a project, but am not sure where to start.

gorgoiler• 5 years ago

Fantastic.

watch for hours

The call time on the incline elevator… wow you weren’t kidding.

Also, at 5m40s is that a domestic clock being used for station timekeeping? Such a shame given the rest of the station design and the amount of time and money that went into it all. Details, people. Details :)

codetrotter• 5 years ago

Here’s another couple pretty random Fandom wikis that I came across just recently. Linking the specific pages I landed on them at.

https://allspecies.fandom.com/wiki/Bogdanoff_Twins

A fandom wiki about “all species” and it has just short of 1k articles about everything from these two guys to fictional species such as Alien.

https://monstercat.fandom.com/wiki/Crab_Rave

This one is specifically about the music label Monstercat. It has about 4k pages.

swiley• 5 years ago

Are you aware of the vim fandom?

It seems to be one of the more complete vim wikis and it's probably the most annoying wiki for a piece of open source software ever. I often go without using whatever information is on there just to avoid listening to my fans (heh) spin up.

anthk• 5 years ago

Use lynx/links for that wiki.

fansub• 5 years ago

Fandom was formerly known as Wikia, the commercial platform launched by Jimmy Wales. This wiki (along with many others) was launched long before the Fandom name.

smegger0012• 5 years ago

yeah i don't know why they switched everything from wikia to fandom i think it was a bad call.

DonHopkins8• 5 years ago

My experience at science fiction fandom conventions is that a large proportion of everyone's time is spent in elevators.

SilverRed• 5 years ago

I was impressed and disappointed at the same time. I wanted to find a page explaining the safeties and failure modes of elevators but I didn't find anything.

Animats2• 5 years ago

Here's a simple explanation of elevator overspeed safeties.[1]

[1] https://youtu.be/UgEL6aeGUrQ

dbcurtis3• 5 years ago

Pfft. List is far from complete. I have done 3rd party interfaces to several elevator controllers. I am highly encumbered by NDA’s, so won’t say much. But I still wonder what “Korean Lunch 2” mode does???

iratewizard• 5 years ago

Ah, yes. The mode that fills the elevator with vinegar and waits for the passengers to ferment.

rossdavidh2• 5 years ago

I live in a warm climate and can confirm that sometimes the passengers do start fermenting, if it's summer in the middle of the day.

hooplah• 5 years ago

Wouldn't that most likely be derivative of a peak mode (either up or down).

Park at top, open doors, wait for traffic down, return up.

Korea Lunch 1 would park at top for people leaving for lunch, 2 would park at bottom for people returning?

jannyfer• 5 years ago

Ooh I've no idea what that would do, but wanted to share something interesting I noticed.

When I visited Korea, I've noticed companies tend to have exact 12-1PM lunchtimes, all at the same time. People raise eyebrows if you leave at 11:50 and return 12:50.

At 12PM, it's hard to grab an elevator going down, so people will press the "up" button to try to catch an empty elevator, then ride it to the top then down to the ground. Vice versa for 1PM.

yjftsjthsd-h• 5 years ago

When I visited Korea, I've noticed companies tend to have exact 12-1PM lunchtimes, all at the same time. People raise eyebrows if you leave at 11:50 and return 12:50.

It just seems so inefficient to do it that way? In theory, I guess the company sorta benefits from having everyone on/off at once, but doing it like that basically guarantees traffic jams.

neolog• 5 years ago

so won’t say much

can you say something though?

rightbyte• 5 years ago

I wish 'hold to deselect' was standard. It only works on some elevators and it can be quite annoying if some kid presses all floors ...

jackbeck4• 5 years ago

I found that on some elevators a quick double press cancels a selection.

dqv• 5 years ago

Since we’re talking about elevators, it would appear anyone can call the elevator’s emergency phone line. Which is good, but also has unintended consequences: https://vm.tiktok.com/ZMdXyQ5ra/

nextlevelwizard6• 5 years ago

Depends on model and implementation. Usually these days the alarm phone will not pick up calls from any number (allow list used), but this looks like older car, so this might be retrofitted and/or maybe some software rules were not set during installation.

sam_goody• 5 years ago

There was a story of a guy who got stuck in an elevator and called for help, but the installer had gone bust and the number had been assigned to a psychiatrist in another county. At first the therapist claimed he couldn't do anything, but when the man pleaded for help, the therapist replied "Well, how does it feel to be trapped in an elevator."...

ortusdux• 5 years ago

I had read somewhere that holding the boor close button along with your desired floor button will override the que in many elevators, taking you directly to that floor. I successfully tested the button combo in the elevator in my building. It came in handy when a kid pressed all the buttons and then stuck his tongue out at me.

mmastrac3• 5 years ago

My university had an elevator with a special three-button keypress that took you to a dark sub-basement full of asbestos warnings and terrifyingly dark that wasn't listed on the display.

_squared_• 5 years ago

You should have explored a bit, might be cake down there

rognjen2• 5 years ago

I heard it's a lie

exikyut2• 5 years ago

So you'd hold down all 3 buttons at once, or press them in a specific sequence, or...?

When you did this, did the floor indicator show anything different?

And where (what country) was this?

mmastrac3• 5 years ago

It was three floor buttons at the same time. I cannot recall what the floor indicator said, but the elevator was quite old and might not have even had one.

This was at the University of Calgary, engineering buildings (circa 2000)

geephroh• 5 years ago

Slightly off-topic, but I'd definitely recommend Colson Whitehead's _The Intuitionist_[1] for anyone interested in the intersection of elevators and speculative mysteries. Never thought I'd get the chance to post this to an HN thread...

[1] https://en.wikipedia.org/wiki/The_Intuitionist

splatzone• 5 years ago

It’s really nice to get some fiction recommendations from HN! Looking forward to reading this

FooBarBizBazz3• 5 years ago

One of my first thoughts too. I preferred John Henry Days, but whatever. As for The Intuitionist -- the whole thing is kind of a troll. Like, the premise is absurd. Of course, that's sort of the point.

llampx• 5 years ago

I wondered why, during the pandemic, it wasn't common to let elevators "air out" while they were idle. Given what we know about COVID-19 and how it spreads with aerosols. From looking at this list, it appears that that's not a mode they would have by default.

galago• 5 years ago

I work in an office building that's less than 5 years old. During the pandemic the elevators started returning to the ground floor and opening their doors. I wonder if the system is configured via the control panel in the elevator or if there's some other interface.

jakemal• 5 years ago

Sounds like it was in up-peak mode? https://elevation.fandom.com/wiki/Up_peak_(MIT)

nextlevelwizard6• 5 years ago

As someone who works in the elevator industry this list is pretty odd and is missing many modes that I would consider default modes.

However to get back to "airing the elevator out". Do you mean just not closing doors after serving a call? Maybe having someone timeout after serving a call to not move? Or actually installing fans to blow out the air?

piceas• 5 years ago

In my building the elevator returns to ground. My preference would be to simply have the doors left open closest to the source of fresh air.

natch• 5 years ago

I’ll just leave this here… I love this guy, he is so passionate about mechanical stuff. A bit on the odd side but a lot of heart.

https://youtube.com/c/WestCoastElevators

teruakohatu• 5 years ago

If says this about 'Pet Mode'

Does not infect other passengers if the animal has an infection

I think this must be a mistranslation. There are very few infectious diseases that a human can get from being around a house pet. I think they mean allergies.

DonHopkins8• 5 years ago

Rabies?

user-the-name• 5 years ago

Other pets can, though.

matsemann• 5 years ago

Related, Elevator Saga. https://news.ycombinator.com/item?id=27487111

A game where you program the logic of elevators to move people around efficiently. Surprisingly complicated.

FooBarBizBazz3• 5 years ago

I've heard this is a legit job for people with serious Operations Research qualifications.

1024core• 5 years ago

I found a "mode" in an elevator in India that I have not seen anywhere else: if a destination floor number is highlighted, and you press it twice, it gets cancelled. I have used this magic power just once, when an obnoxious man got on and insisted on having a loud conversation on his phone. Since he wasn't paying attention, I double-tapped his floor number and made him skip. I happened to get off at the floor before his, so the elevator went down to the first floor after dropping me off. Small pleasures....

63• 5 years ago

I believe your story highlights precisely why more elevators don't include that functionality.

cunthorpe2• 5 years ago

No it doesn't. You can't prevent people from being a-holes and stealthily pressing 10 buttons before leaving the elevator. The feature as described is as useful as pressing a floor to stop on. Perhaps it makes more sense on smaller elevators than it does in large ones. Or perhaps it would make more sense to allow undoing a press only within the first few seconds.

graup• 5 years ago

In South Korea, pretty much all elevators have this enabled. Pressing a floor button a second time cancels the request. It's pretty useful (if not abused).

urbandw311er• 5 years ago

This has made my day. I have spent much of the last decade campaigning to anyone who would listen for the existence of a feature such of this to nullify accidental button presses in an elevator.

cunthorpe2• 5 years ago

I literally used that feature earlier today in an elevator in Thailand. The exact method of operation seems to vary among elevators, some require you to hold it, others require more than 2 presses. It's great when you change your mind.

mahathu• 5 years ago

you can have phone conversations in a lift cabin? don't they act like faraday cages? I always lose connection in mine.

gregoriol• 5 years ago

This could be a nice "learning" trick too: sometimes, you see people pressing angrily on buttons many times when they are in a hurry, this teaches them to cool down, don't press the button many times, it won't help.

rognjen2• 5 years ago

In my experience in Asia it's about 50-50 chance that it's either double-press, long press or second press that cancels it or that it's not enabled.

sillysaurusx• 5 years ago

One time when working as a pentester, we were doing redteaming (read: breaking into target buildings, physically). Well, they were doing redteaming; I always wanted to, but never quite got the opportunity.

One of the ideas thrown around for achieving the objective was to somehow get ahold of an elevator key, stop it, and hide in there until the building closed.

I don't know if they actually did that, but it would've been hilarious to see them pop out like a scoobie doo villain and jack into an ethernet port while the janitor has no idea what's going on.

542458• 5 years ago

There’s a legendary defcon talk about elevators where the speaker describes doing exactly that on several occasions. Searching “Defcon Elevator” on YouTube should pull up the video in question.

bombcar• 5 years ago

“Somehow get an elevator key” is very easy - they’re all the same (at least the fireman’s are).

mpd• 5 years ago

I ran into https://www.youtube.com/watch?v=ZUvGfuLlZus (Elevator Hacking: From the Pit to the Penthouse) awhile back, and it was so interesting to me that I ended up watching the entire 2 hours in one sitting.

banana_giraffe• 5 years ago

Another such list is on Wikipedia: https://en.wikipedia.org/wiki/Elevator#Special_operating_mod...

Wiki lists a "Riot mode", which is just amazing if it's a thing.

nextlevelwizard6• 5 years ago

It has different names on different manufacturers, but yes it is a thing.

svat2• 5 years ago

Donald Knuth's The Art of Computer Programming has, in its first volume, a lengthy section on simulating an elevator. It is a single regular elevator (nothing "special" going on as in the post here), but even so, as he tries to make things precise, you realize how much detail is involved, and get some appreciation for the task of programming.

It occupies about 15 pages (plus several pages of exercises and solutions). Knuth started working on TAOCP when he was a PhD student at Caltech:

The program developed below simulates the elevator system in the Mathematics building of the California Institute of Technology. The results of such a simulation will perhaps be of use only to people who make reasonably frequent visits to Caltech; and even for them, it may be simpler just to try using the elevator several times instead of writing a computer program. […]
The algorithm we will now study may not reflect the elevator’s true principles of operation, but it is believed to be the simplest set of rules that explain all the phenomena observed during several hours of experimentation by the author during the writing of this section. […]
The elevator system described above is quite complicated by comparison with other algorithms we have seen in this book, but the choice of a real-life system is more typical of a simulation problem than any cooked-up “textbook example” would ever be.

It ends with:

It is hoped that some reader will learn as much about simulation from the example above as the author learned about elevators while the example was being prepared.

And one of the exercises adds:

It is perhaps significant to note that although the author had used the elevator system for years and thought he knew it well, it wasn’t until he attempted to write this section that he realized there were quite a few facts about the elevator’s system of choosing directions that he did not know. He went back to experiment with the elevator six separate times, each time believing he had finally achieved a complete understanding of its modus operandi. (Now he is reluctant to ride it for fear that some new facet of its operation will appear, contradicting the algorithms given.) We often fail to realize how little we know about a thing until we attempt to simulate it on a computer.

iaw• 5 years ago

We often fail to realize how little we know about a thing until we attempt to simulate it on a computer.

I'll often write out with pen and paper of how I think the flow of a model will go, it's always fascinating how much that diagram changes once I actually build the model. There are both drastic simplifications and increases in nuance based on experience with the system being modeled and where divergences occur.

TeMPOraL2• 5 years ago

Same here. And this also works for existing code. When I start diagramming some complex bit of flow, I'm often surprised by how little I actually understood it. I think translating to a different medium of expression forces you to actually read the code, instead of just skimming it and thinking you understand it.

pram• 5 years ago

If you love elevators try out SimTower, it's all about micromanaging them!

ben_bai• 5 years ago

SimTower started as elevator simulator, and was then turned into a game.

Also, this is a great talk if you want to know more about elevators: https://www.youtube.com/watch?v=ZUvGfuLlZus

jhgb• 5 years ago

We often fail to realize how little we know about a thing until we attempt to simulate it on a computer.

"Programming is a good medium for expressing poorly understood and sloppily formulated ideas" is definitely on the list of my favourite programming quotes.

fho• 5 years ago

I recently tried to implement a simple version of an existing board game ... boy did all those "if you have this card and I have that card except for that special condition and also none of this matters if you play this card" bite me in the end ...

rablackburn• 5 years ago

Slightly relevant story time:

On one of the better teams I’ve worked with the water-cooler activity was trying to come up with an algorithm to describe the behaviour of the Coca Cola machine in the kitchen.

It was one of those clear plexiglass front machines where after punching in the coordinates of the item you wanted, a mechanical arm would move to the coordinates, take a drink, and place it in the delivery bay at the bottom.

While it would always get the drink you wanted, it would rarely go to the exact coordinates you specified. Ie, if there were three columns filled with coke, and you punched in the coordinates for the one on the far right, the arm may take a can from the center, or left column.

We would often wager a can of coke (“if I can’t find anything wrong in your PR, I’ll buy you a coke”), so we were perhaps drinking more soft drink than was medically advisable, but in our defence:

a) the machine was really cheap (AUD$1 or $1.5)

b) it was an excellent 10min break game

Eventually we thought they had it figured out we would gather and make our predictions, but occasionally there would be an upset that would throw a wrench into the model.

We got to a point where we just couldn’t reconcile the machine behaviour with any kind of coherent set of rules, then one morning we saw the delivery guy stocking it.

After chatting with him we learned our algorithm was more or less correct, but the internal state of the machine was prone to getting out of sync with the actual stock levels, so it would make the “wrong” choice near the end of the refill cycle. Then he gave the engineer talking to him a free energy drink (source of stock problems right there haha)

While we were no Knuths, I love that these kinds of games are so universal among engineers/devs. In fact, if I can get someone to tell me a similar story of theirs in an interview (for a technical role) I’m much more likely to consider them for the position. Curiosity is a powerful trait for a developer.

…and the (simple) algorithm for the machine is: Take from the column with the most stock, if there are multiple columns with the same stock level, take from the column furthest to the left.

grishka3• 5 years ago

Hm. I've always thought that the algorithm of operation of a single elevator is fairly simple? While passing each floor, if a button of that floor was pressed (is lit up), or if the button of the direction it's going on that floor is pressed, then stop. If the elevator is not in use and someone presses any call button, go to that floor. That's mostly it. At least that's how I have that algorithm in my head.

Now, if there are multiple elevators but a single set of up/down buttons for them on each floor, that's where things get really complex really fast.

saila• 5 years ago

What if you have, say, a 7 story building and someone on each floor presses the call button at around the same time? Do you send the elevator to each floor based on the time the button was pressed, or do you maybe go to the top floor and pick everyone up on the way down, or do something else? The algorithm probably also needs to consider max weight/occupancy. I think even for a single elevator it's quite complex, assuming you want operation to be both fair and efficient.

svat2• 5 years ago

Yes that's mostly it for such old elevators (see "Elevator algorithm" https://en.wikipedia.org/w/index.php?title=Elevator&oldid=10...), except:

- The elevator has a "home floor" (the lobby/ground floor) that it returns to by default, if it has nothing else to do. (Apparently many elevators do this; see "Up peak" in the linked post or on Wikipedia https://en.wikipedia.org/w/index.php?title=Elevator&oldid=10... .)

- To set up such a discrete event simulation on a computer, you also need to model timing (how much time it takes to open and close doors, to move between floors with acceleration/deceleration, etc), and users (how many arrive at each floor and when, and where they want to go to, how long they wait before giving up).

- So you end up with a fair amount of state (the "up" and "down" call buttons on each floor, the buttons inside the elevator, whether the elevator is going up or down or neither) and control (when to open or close doors: what to do if someone presses a button while the doors are closing, etc).

- The purpose of that section of TAOCP is to show in detail how to use doubly-linked lists to simulate such things on a computer (which here means getting down to the level of memory layout and assembly code: MIX/MMIX). So overall there are ~5.5 pages of describing the algorithm, ~1.5 pages for memory layout etc, ~7 pages of assembly code, and a page of higher-level stuff mentioning programming languages and profilers etc.

I'm aware of two repositories on GitHub that reproduce this simulation in a higher-level language: https://github.com/meatfighter/knuth-elevator (700-odd lines of Go code including comments from TAOCP) and https://github.com/Quuxplusone/KnuthElevator (500-odd lines of C++14 code without the copied comments). (Learned of the latter via https://www.meetup.com/theartofcomputerprogramming/ a meetup for reading TAOCP.)

trhway• 5 years ago

"pet mode" reminded about my cat many years ago - we lived on the 5th floor of an apartment building, and going outside the cat would walk the stairs down, yet coming back the cat would sit near elevator on the ground floor until somebody would come to use the elevator and everybody knew that "the white cat rides to the 5th floor" so they would let him out there.

grensley• 5 years ago

My favorite interview question is "how do elevators work"?

0. If they immediately blurt out something like "I know how elevators work", probably don't hire them.

1. You can find out what areas they're most interested in. Do they jump straight to the physical mechanics? The programming? The UI? The abstraction that they're solving a problem?

2. Eventually, they reach a point where they just have to say "I don't know". The rabbit hole really just keeps going with elevators. You could know this question is coming and we will still easily reach the knowledge boundary.

3. If they "don't know" you can ask them to guess how a system might work. Or give them time to research it and follow up with you later.

flycaliguy• 5 years ago

I did a design interview which involved drawing up an elevator control panel for an apartment building with 1000 floors. Me, trying to leverage my sense of humour I guess (oops) designed a system in which the presumed wealthiest users at the top were instantly recognized with a face scan and never had to see a panel of buttons. The rest were forced to use a basic number pad. Needless to say I didn’t get the job. Doesn’t help that when you google my name my father’s extensive work as a labour organizer tends to spook my potential boss…

TeMPOraL2• 5 years ago

Your idea reminds me of a recent novella by Cory Doctorow, Unauthorized Bread. In there, there was an apartment tower with an elevator that had separate doors for poor and rich people (with the two groups living on different floors), and the poor people couldn't call the elevator when it was in use by the rich.

lozf• 5 years ago

Deviant Ollam & Howard Payne did a great talk on Elevator Hacking at Def Con 22.

You can catch it at:

https://archive.org/details/Defcon22_Talk29/DEF+CON+22+Hacki...

https://www.youtube.com/watch?v=oHf1vD5_b5I [01:00:15]

BigJono• 5 years ago

This is one of my favourite talks ever. I couldn't have given less of a shit about the topic and wasn't expecting to watch more than 5 minutes of it. Nek minnut the video is ending and I wanted another hour of it haha.

dlgeek• 5 years ago

Look for "This key is your key, this key is my key" by the same pair. It's basically that.

rozab• 5 years ago

Deviant Ollam's talks are always first class. I also love this one, about physical pentesting in general:

https://youtu.be/rnmcRTnTNC8

aaron695• 5 years ago

Not sure if it's still true, but if to pick up the emergence phone (but don't push the call button) you could often use DTMF tones to call a number for free.

tgsovlerkhgsel• 5 years ago

The elevator in my building only lets you select one floor. Accidentally press the one above yours? Now you have to go there first.

Any idea what the purpose of that is? Price discrimination? Abuse prevention? "Well, the ancient elevator did it that way and we want the new one to be the same" backwards "compatibility"?

nextlevelwizard6• 5 years ago

Probably extremely aggressive nuisance prevention. You could try holding the wrongly selected button down for 3-5 seconds and see if that cancels the call so you can give another one.

theHIDninja• 5 years ago

There is also riot mode, where it won't stop on the first floor. It's used to stop people from just running in off the street and using elevators.

nextlevelwizard6• 5 years ago

The floor or set of floors is usually configurable these days. Since in modern buildings you can have multiple entrance floors.

k12sosse2• 5 years ago

I was electrocuted fucking around with an old elevator once. Now I just get on it and travel to my destination. :) A very humbling experience to have happen in front of your peers.

ummwhat• 5 years ago

You were electroshocked. It's only electrocution if you die.

k12sosse2• 5 years ago

Neat, thank you for electroclarifying!

teameat• 5 years ago

Another dumb story from "back in my day". When I was in college way back in 1976, me and my Best friend back then both had graduated early and had to live in the dorm the first year until we were 18. The dorm they made us stay in was 6 stories and had a crappy old elevator. Being a couple of goofy hacker types with nothing better to do on a weekend, we figured out how to get up on top of the elevator and to use the alternate control panel up there. We sat up there and could control it, people would get on, we could listen to them talk, stop the elevator between floors and they would get all scared, we would flicker the lights on and off, make it go to the wrong floor and so forth. Pretty fun stuff for a couple of nerds.

We got bored with that pretty quickly until, 4 gals form the girls floor decided they were going to camp out in there and set the Guinness record for the longest stay in an elevator. Some of the bigger dudes knew that we had hacked the elevator and asked us if we wanted to mess them up. Well... Of course. So we got on top and were listen to them yakkedy yak. Then we took it to between the 6th and 5th floors and locked it in place, then opened the upper doors on the 6th floor where a bunch of guys with big trash cans full of water were waiting.

We thought they were just going to douse them good. So we opened the ceiling trap door to the elevator with the lights off and those gals were screaming and squealing like crazy. Then come dude tossed a string of fire crackers in there followed by two giant Garbage cans of water right after that. Must have been at least a couple hundred gallons of water, who knows.

Then we set the thing to go to the first floor and jumped off. Waiting on the first floor where a bunch of people who were in on it with cameras to capture the whole things as the doors opened it was like the seas parting and flooding out as these poor drenched young ladies came floating out. Picture was on the front page of the school paper "Guinness Elevator Record Attempt Drenched" or something.

They called the cops and all that but no one squealed on us and it was all in good fun but to teach everyone a lesson they shut down the elevators for 3 weeks. Young people don't care, worth a climb of the stairs for all the fun!

BTW, I ended up marrying one of the gals on the elevator and yes I told her I was in on it, later. She loved that for some reason :)

smabie• 5 years ago

A+ story loved it!

MockObject• 5 years ago

I don't know why this excellent story is getting downvoted. Thanks for sharing it. It's great that she had a good sense of humor about everything.

vintermann• 5 years ago

ALMOST HUMAN

    The thinking elevator,
    so the makers proudly say,
    will optimize its program
    in an almost human way.
    And truly, the resemblance
    is uncomfortably strong:
    it isn't merely thinking,
    it is even thinking wrong.

(Piet Hein, 1973)

praptak2• 5 years ago

The elevator in the apartment building I currently live in has a quirk which adds ~2s to the travel. If you know this quirk you can save the ~2s on each use.

So if you just pick the floor then it waits 2 seconds before closing the door. Obviously the elevator waits for the door to get fully shut before it starts moving.

If you first press the "shut door" button and then the floor button, then the door shuts within any delays, which means the elevator starts moving 2 seconds earlier.

AnssiH• 5 years ago

Interesting. Mine has an even longer delay than 2s (3-4s?) so I always press the close-doors button which removes the delay, but it never occurred to me I could shave some additional milliseconds off by pressing the close-doors button before the floor selection button.

praptak2• 5 years ago

In my case pressing the close-doors button after the floor button does not do anything - it is as if the floor button sets the timer on the doors, which then cannot be changed by the close-doors button.

List of Special Elevator Modes

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