How does the calculator percent key work? (2008)

http://blogs.msdn.com/b/oldnewthing/archive/2008/01/10/7047497.aspx

by vmarsy • 11 years ago

128 57 11 years ago

blogs.msdn.com

evolve2k• 11 years ago

So I worked for over 10 years as an Accountant/CPA and over 6 years as a coder and all this time I've never know how to use that damn key. Thanks!

stevecalifornia• 11 years ago

I wish I had known this 20 years ago. Something so simple and so useful.

thaumasiotes2• 11 years ago

Is it really more simple to type "72 + 5 %" than to type "72 * 1.05"?

copperx2• 11 years ago

It is. It saves you from an extra mental operation. What's the price of that $56 shirt after 22% off? Doing 1-22/100 in your head adds an extra possibility for error.

bitwize• 11 years ago

If you don't know math, then yes. Most people don't know or care that "adding 5% tax" is equivalent to multiplying by 1.05. They just know that you have to add 5% for tax. So 72 + 5% makes perfect sense; 72 * 1.05 is terribly confusing.

kleer001• 11 years ago

Whoa, that's a lot more complicated than I give calculators for being.

jtbarrett• 11 years ago

If you're tying to follow along in calc.exe but the percent key is disabled, switch to Standard mode. It's not on in the other modes.

joshschreuder• 11 years ago

Oddly enough, on Windows 8 it appears in Scientific and Programmer modes but is greyed out, and I couldn't get it to activate. Why not hide it?

agarcia-deniz• 11 years ago

just noticed that myself, had pretty much the same thought.

userbinator4• 11 years ago

...or why not make it usable in all modes?

I think the calculator in Windows 7 and above took a seriously backwards step in functionality - they seem to have thought that programmers don't need exponentiation nor square roots nor floating-point(!), so there is no such function in "programmer mode" and you cannot change the number base in "scientific mode". That would only be a minor annoyance, if not for the fact that switching between modes clears the accumulator!

http://answers.microsoft.com/en-us/windows/forum/windows_7-w...

It is a classic case of too much modality in UI design. The first time I discovered this "feature" after losing the result of a long calculation, I thought it was a bug or I'd accidentally hit the wrong key. When I found out this was by design, it elicited a loud enough "WTF!?" that caught my co-workers attentions and caused them to exclaim the same thing after showing it to them. Fortunately the calc.exe from XP runs fine on 7 and 8.

There's another "feature" which I hadn't personally run into, but would be just as incensed if I did:

https://social.technet.microsoft.com/Forums/windows/en-US/4e...

DonHopkins• 11 years ago

Dang, and I always thought it was to show the percentage of battery power left.

vt240• 11 years ago

That is fantastic, something I never would have thought of!

nextos• 11 years ago

The Windows calculator percent sign works the same way as those cheap pocket calculators

I never understood how these cheap calculators worked. I'm glad most serious desktop calculator apps, like the OS X one, have a RPN mode. As a high schooler, my dad forced me to switch to RPN calculators when we began doing very lengthy calculations.

People thought I was a freak. But in retrospect, it was an awesome decision. With a stack, things are much simpler. You don't need those clumsy memory registers or parentheses, and all operators have a very simple semantics.

As a bonus point, an innocent looking HP15C implements or can implement quite advanced numerical methods. It was a secret retro weapon from the 80s when all they allowed were non-graphical calculators.

lambdaelite• 11 years ago

After years of using an HP, I am literally unable to use anything but RPN without significant conscious thought. I'm faster with pencil and paper (or an abacus!) than using a non-RPN calculator at this point.

mintplant• 11 years ago

Any recommendations for a good RPN calculator on Linux?

tokenrove• 11 years ago

M-x calc in emacs

lambda4• 11 years ago

I generally just use dc on the command line. Pretty bare bones, but gets the job done.

M-x calc in Emacs is a very full-featured RPN calculator.

On Android, I use Droid48, a great HP48 emulator: https://play.google.com/store/apps/details?id=org.ab.x48 ; I also have RealCalc (https://play.google.com/store/apps/details?id=uk.co.nickfine...) installed, which I figured I'd use more due to the bigger buttons by default, but I still reach for Droid48 most often.

SixSigma• 11 years ago

forth

lultimouomo• 11 years ago

I use galculator quite regularly, it has a pretty decent RPN mode.

cbd1984• 11 years ago

My HP-48GX is just as secret-weapon-ish in its fierce programmability. ;)

I'm pretty sure you can access every feature the calculator has from its stack, which means they're all available for use in programs; it also comes with a nice equation library full of physics equations with helpful diagrams and information about what various variables are.

Quite amazing for the time, and still very useful. It's frugal with batteries, too.

copperx2• 11 years ago

The HP-48G is a lovely machine, although it's quite slow. Is the HP-48GX better? Graphing anything takes ages.

userbinator4• 11 years ago

I never understood how these cheap calculators worked.

They are usually based on the two-register model, or at least the very very simplest ones: one accumulator, R, holds the "result"; another accumulator, I, holds the input. The button CE clears I to 0, and C clears R to 0. The display always shows the contents of the most recently modified accumulator. An "operation" register, O, contains the most recently pressed operation button and is initially the null operation. Inputting digits/decimal points modifies I.

Whenever +, -, , / are entered, it performs R = R O I and then sets O to the new most recent operation. When '=' is pressed, R = R O I without changing the most recent operation. This is why sequences like 1+2+54= gives 32, and then '=' again will multiply 32 by 4, etc.

This type of calculator is easy to identify because it has no notion of operator precedence and always evaluates in the sequence it's given, and furthermore doesn't actually require an '=' key - observe that if e.g. you input 2+2-, 2+2+, 2+2/, or 2+2*, the display already shows 4 because entering the last op has caused the previous op + to be evaluated giving R += I, and the display shows the new value of R.

Those with a "memory" function add another accumulator, M. Then the operation MC is M=0, M+ performs M+=R or M+=I (depending on the currently displayed register), M- is M-=R or M-=I, and MR is I=M.

userbinator4• 11 years ago

Also, in terms of this register machine the percent key performs the operation I = R * I /100, and modifying I causes the display to show the new value of I just like the article mentions:

When the user enters a value, an operator, a second value, and then the percent key, the first two values are multiplied and the product divided by 100, and that result replaces the second value in the ongoing computation.

If you watch the display as you go through this exercise, you will even see the number 3.6 appear in the display once you press the % key. The percentage is calculated and replaces the original value in the ongoing computation.

cbhl• 11 years ago

Hacker News uses asterisks for italics. Consider replacing some of them with 'x'es.

thaumasiotes2• 11 years ago

I used to have a cheap pocket calculator, but what I determined through experimentation was that pressing % caused whatever number was on the display to be immediately divided by 100.

It's possible, I guess, that I just never found out how to use % in the intended manner, but it was pretty surprising to me to see it referred to as common knowledge that four-function calculators were supposedly doing magic with the % key behind the scenes.

sliverstorm• 11 years ago

With a stack, things are much simpler.

Exactly how I feel about MtG (end tangent)

PebblesHD• 11 years ago

I've always found it best to stick with a pleasent middle ground. I use a Casio fx82au-plus and it has enough complexity and functionality to suit my needs whilst behaving as expected when anyone in the office asks to borrow a calculator. Otherwise, my iPhone is perfectly capable...

Dylan16807• 11 years ago

With a stack, things are much simpler. You don't need those clumsy memory registers or parentheses

You can prefer RPN all you like, but to think it's objectively better and that parentheses are flat-out bad is crazy. It's a tradeoff. The action of each key is slightly simpler, but you are forced to reorder your equation to change operator application. Sometimes this means keeping track of fewer parts, but sometimes it means keeping track of more.

jonsen3• 11 years ago

Try this on a non-RPN calculator

  3 + 4   7 + 8
  ----- + -----
  5 + 6   9 + 2

PhantomGremlin• 11 years ago

I'm glad most serious desktop calculator apps, like the OS X one, have a RPN mode

I've loved RPN since around 1973 when I paid $395 (plus 7% tax) for an HP-45. I still have an HP-42S that I use.

However, I often find it easier in OS X to just type "python" and go from there. I love Python as an interactive interpreter. It's easy to give good names to intermediate variables. Functions are easily created, starting with "def ...". Etc.

But this works for me because I rarely need sin(), cos(), or stuff like that. It would get tedious to load the Python math functions, to remember the exact spelling of a function. A calculator is good for that, because the keys are right in front of your face. Can't miss 'em.

glogla• 11 years ago

Exactly. I long time used bc or bc -l but python is more flexible, and with readline, much more practical than button based calculator.

kelnos• 11 years ago

But this works for me because I rarely need sin(), cos(), or stuff like that. It would get tedious to load the Python math functions, to remember the exact spelling of a function.

Most of these are pretty easy -- just do "from math import *" and then you have sin(), cos(), etc. imported into the root namespace.

If you want to explore, you can use something like bpython, do "import math", and just type "math." and it'll pop up a little window showing you the possibilities.

WalterBright• 11 years ago

What a waste of a key.

It's like those miserable cheat sheets for electronics that contain:

    V=IR
    R=V/I
    I=V/R

First off, if you don't know Ohm's Law you have no business doing anything with electronics - you're going to use the formulas wrongly. Secondly, if you can't trivially derive the various forms in your head, you have no business using them.

cdcarter• 11 years ago

This makes me desperately miss my register tape 10-key at my old desk. I wish I could find an iPhone app that acts like a 10-key adding machine.

donatj• 11 years ago

I am honestly kind of shocked at the responses to this. We used it in school, I used it at home to figure out sales tax as a kid, I'm honestly shocked so many people don't know what the percent button on a calculator does.

JacobAldridge• 11 years ago

Many HNers are just part of today's lucky 10,000.

https://xkcd.com/1053/

pluma3• 11 years ago

I had no idea because we learned to convert percentages before we were allowed to use calculators in school. So by the time we could have used the % button it was already second nature to read "x + 5%" as "x * 1.05".

kokey• 11 years ago

I used the % on the calculator as a kid a lot. Then for about 25 years I didn't touch a desktop calculator and was thinking in 75 x 1.05, so when I recently tried to use the percentage sign it didn't work intuitively for me. I tried 75 x 5% and that certainly gave me an answer that felt wrong.

GFK_of_xmaspast• 11 years ago

I thought hackers were famed for experimenting with hardware and interfaces and trying to ferret out all the secrets.

traditionals• 11 years ago

But I never wanted a button that worked like that.

That's not what I care about when calculating percentages.

I don't want an inlined relative percentile value, based on prior terms. I almost never need that, and thus never use the percentage key, because that makes it useless and the behavior is counter intuitive.

What if I have a much longer chain of calculations to tally up? What I need, then, is a percentage for one of the terms in isolation, BEFORE I start calculating.

If I have an arbitrarily large number, and an arbitrarily complex percentile value, which makes the percentile value difficult to determine in one's head, I want a button that performs as follows:

  37.82726419 percent of 9999.928374666666 equals ???

Which gets keyed as:

  37.82726419 % 9999.928374666666 = ???

Then, I take that number and roll it into any other subsequent equations.

Too bad the button will never ever work that way, because "tradition."

How does the calculator percent key work? (2008)

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