Exhaustive, commented, list of units

by btilly • 16 years ago

45 33 16 years ago

btilly5• 16 years ago

Check it out if for no other reason than to read the rant about how poorly defined the candela is.

DrJokepu• 16 years ago

Also, it's really hard to resist the temptation to "rant back" on the kilogram question. Unfortunately / fortunately, HN comments are not the right place for that.

(Basically, kg is the perfect unit of mass and if you disagree you are a heathen and should be burned)

btilly5• 16 years ago

His complaint is that if kg is the perfect unit of mass then make what we call the kg be the base unit and call that a gram instead. Makes perfect sense to me.

Of course this is an imperfect world. In a perfect world I'd like a meter chosen so that gravity is, to a good approximation, 1 m/s at sea level, and I'd like all of the units to be in base 12. (Easy divisibility by 3 is often very useful.) Including time, so that one doesn't have the awkward 3.6 factor converting from m/s to km/h. And our number system should also be base 12, and...I think you can see that I'm willing to complain about lots of things which will never change.

redcap• 16 years ago

energy := c^2 // convert mass to energy

Looks like it's missing some mass.

btilly5• 16 years ago

You're right. I just emailed a bug report.

monkey• 16 years ago

Thanks for the report, but this shouldn't be considered a bug. That unit is defined so that you can write "1 gram energy" or the like to find the energy content in that particular amount of mass. It's actually shorter (on a reasonable keyboard) to type "c^2" though, so this may not really be necessary. I may remove it from the data file.

sesqu• 16 years ago

There's also a comment in Kelvin regarding how the triple point of water is defined to be at 0.01 °C, not 0 °C, that reads a little confused. I wonder why it's defined like that, anyway.

The bit is used for information because information is almost defined as the expected length of an optimally (context-free) coded word, using a base 2 code. Some physicists prefer base e, in which case it's measured in nats.

bluesmoon3• 16 years ago

the triple point of water is defined as 0.01 °C in order for a difference of 1 °C to be equal to a difference of 1 K.

To put it another way, the triple point of water is known to be 273.16 K, and the boiling point 373.15 K. Now if this mapped on to 0 °C and 100 °C, then we'd be left with a situation where 100 kelvins would be equivalent to 100.01 Celsius degrees. Instead, by defining the triple point of water as 0.01 °C (still 273.16 K), we now get an interval of 100 kelvins being equal to an interval of 100 Celsius degrees.

This is also why the term centigrade is no longer used... it's no longer 100 even.

jerf• 16 years ago

Relativity unified some of the elementary units in surprising ways that make this sort of file hard to write if you really, really want to be rigidly correct. Technically, in some sense, "time" and "length" shouldn't both be atomic units, we should have only one or the other. But that would make this less useful, even if more accurate.

jarin• 16 years ago

It's not a complete list of units without the hella- prefix.

tome• 16 years ago

hellacandela?

bluesmoon3• 16 years ago

what? no Helens

    beauty =!= H
    Helen := H      // The beauty required to launch a 1000 ships
                    // A mH is the beauty required to launch 1 ship

philwelch• 16 years ago

Wouldn't that be a mH (milli-Helen)? A micro-Helen would only launch 1/1,000th of a ship, so perhaps a kayak or life raft.

bluesmoon3• 16 years ago

yep, my mistake, will fix

JeanPierre• 16 years ago

If we're going with these...

  1 Potrzebie := 2.263348517438173216473 mm // thickness of Mad issue #26
  1 donkeypower := 1/3 horsepower

user24• 16 years ago

It's also missing the batman unit - http://en.wikipedia.org/wiki/Batman_(unit)

aston• 16 years ago

Seems to be missing

  hella ::- 1ee27    // Northern California slang for "lots of" or "very"

http://www.popsci.com/science/article/2010-03/physics-studen...

RiderOfGiraffes• 16 years ago

It's missing the hundred, an old English measure of area.

gjm11• 16 years ago

It defines "hundred" = 100, and likewise for other spelled-out numbers. I don't think it has any way of making it mean 100 in one context and an area (of, AIUI, indeterminate size) in another.

asmithmd1• 16 years ago

It is missing hardness units: http://en.wikipedia.org/wiki/Shore_durometer http://en.wikipedia.org/wiki/Brinell_hardness

Also roofers commonly refer to a square of shingles:http://wiki.answers.com/Q/How_many_square_feet_will_a_square...

kristiandupont• 16 years ago

Does anybody know why the standard unit for mass is kilograms?

dfox• 16 years ago

THis comes from practical and historical considerations. Mass is probably most commonly used quantity by non-technical people, so it is desirable to maintain continuity with previous systems which had gram as base unit. On the other hand kilogram as base unit makes many useful relations between various quantities simpler not to mention that it is significantly more practical to make and maintain prototype of kilogram, than prototype of gram.

DougWebb• 16 years ago

It's missing the megalithic yard and related units. http://www.ancient-wisdom.co.uk/megalithicyard.htm

This turns out to be a really cool system of measurement involving distance, volume, mass, frequency, etc, all based ultimately on the rotation of the earth.

Edit: the book Urial's Machine and its successors expand a great deal on this system of measurement, and how there are echos of it in Old English and Babylonian measurement systems. I can't find an online description, though.

CERTIORARI• 16 years ago

It's missing Lovelace (Ll), the standard unit of suckiness.

http://www.infonet.ee/~sbernard/asr/computer.html

zck• 16 years ago

There's also the units command: http://www.gnu.org/software/units/units.html

ggbaker• 16 years ago

This file is actually /usr/share/misc/units.dat from units.

roofone• 16 years ago

I'm impressed it has the smoot and evens includes a reference: http://spectrum.lbl.gov/www/personnel/smoot/smoot-measure.ht....

nandemo• 16 years ago

Tangentially related, large named numbers in Japanese:

http://en.wikipedia.org/wiki/Japanese_numerals#Large_numbers

無量大数=muryōtaisū=10^88.

Exhaustive, commented, list of units

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