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Exhaustive, commented, list of units

futureboy.us

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Re: Exhaustive, commented, list of units

#21

Post by dfox »

kristiandupont wrote: post #19

Does anybody know why the standard unit for mass is kilo grams?

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.

Re: Exhaustive, commented, list of units

#23

Post by DougWebb »

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.

Re: Exhaustive, commented, list of units

#24

Post by gjm11 »

RiderOfGiraffes wrote: post #15

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

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.

Re: Exhaustive, commented, list of units

#28

Post by DrJokepu »

btilly wrote: post #2

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

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)

Re: Exhaustive, commented, list of units

#29

Post by jerf »

redcap wrote: post #3

energy := c^2 // convert mass to energy Looks like it's missing some mass.

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.

Re: Exhaustive, commented, list of units

#30

Post by btilly »

DrJokepu wrote: post #28
btilly wrote: post #2

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

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)

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.

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