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Comment by wyager | Hacker News Reader

Never once while studying physics have I been bothered by constant factors, especially nice integer ones like 2. I don't really care if I have to multiply by 2. Feet aren't really different from meters from a physical perspective. The only choice of unit that really has any solid claim to superiority is the natural units.

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> Feet aren't really different from meters from a physical perspective

As a non American I can't help but think if you are doing anything that involves short and long distances feet must surley be painful. Either you use 5280 feet instead of a mile, or 0.000189 miles instead of a foot. And then you have yards...

Madness!

As an American, I have some distant hope that we will switch .. but no sooner than the year 2050

You just switch to miles for anything longer than a few hundred feet. Big units for big things, small units for small things.

The flipside to this I’ve been encountering a lot is engineering drawings in metric for things that are several meters long and all the measurements are in millimeters! Why all the big numbers!

> measurements are in millimeters! Why all the big numbers!

Precision, usually if you are getting something fabricated the numbers are quoted in millimeters if the millimeters is under 10,000. So a desk might be 1800x800x700mm. I don't think I have ever seen something listed as 120000x10000x10000mm. At that point they would switch to meters.

I have so many piles of drawings at work for all sorts of European manufactured machines that are about 6m in length that have their layouts (where mm level precision is silly and pointless) drawn out and measured in mm. 6000mm x 2000mm x 10000mm etc etc. It’s like...why??

As for the precision, I suspect it’s to defeat the perils of floating point numbers in computers...if you only need mm precision, you rather your CNC computer do integer math and not floating point math...am I correct?

Because if everyone millimeters then there is no confusion. For that reason I rarely see anything non-consumer specified in cm.

> CNC computer do integer math and not floating point math...am I correct?

Good point.

> As for the precision, I suspect it’s to defeat the perils of floating point numbers in computers...if you only need mm precision, you rather your CNC computer do integer math and not floating point math...am I correct?

I doubt that. It would be trivial to have the computer convert from 6.000m or 600.0cm to 6000mm internally.

Why not, though? Millimeters are trivial to convert to meters in your head, since you don't need to calculate anything; just move the decimal point.

Using millimeters gives you a "standard precision" which is a boon for interoperability.

>Why not, though?

Because all my tape measures are in inches ;(

You wouldn’t be helped by cm-s either :/

For precision work using inches, decimal thousandths of an inch ('thou') are typically used - for what I assume are similar reasons.

No one ever uses miles and feet together. You just use decimal miles: 5.3 miles, etc.

You use feet for short distances, miles for long.

Or more likely, fractional miles. In Chicago, a standard city block is 1/8 of a mile by 1/16 of a mile (usually the longer dimension is considered a "block" for describing distances since it corresponds to the grid's "hunnerts" for addresses¹, something which confuses my wife to no end, especially when a 3-block walk may cover more or less than 3 physical blocks).

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1. There are a few areas where the hunnerts don't correspond to 1/8 mile blocks: The first mile from Madison to Roosevelt goes from 0 to 1200. Then from 16th to 22nd (Cermak) there are some missing hunnerts and again one missing hunnert between 26th and 31st. Some of these are a consequence of the replatting of the city at the beginning of the twentieth century and some of it, who knows?

a) very few people work on the scale where miles and feet are interconverted.

b) The mistake was picking base-10 as the basis of the metric system. The Base-12/Reciprocal-halves (2^63/2^4) system of feet, inches, fractional inches, is hands-down the best way to engineer and build things on the human scale. It makes it super easy to scale measurements by N/2, N/3, N/4, N/6, N/8, N/12, N/2^m. Three weeks ago had to make 9 evenly spaced holes in a 24' board, with an inch of buffer on either side, which works out to 35-3/4". This results in really convenient interval of N3'-less-N/4" (35-3/4, 71-1/2, 107-1/4, 143"), so convenient I still remember them weeks later.

The yucky part is when you have to use a base(2*5) calculator. Now you get 35.75, 71.5, 107.25, 143", which is a much less obvious pattern.

Every day I'm in the shop, I yearn for a dozenal calculator and measuring tape.

One can dream.

http://www.dozenal.org/

Base 6 is also nice:

http://www.seximal.net

Indeed, the claimed "elegance" of SI doesn't really hold up, with the SI base units now defined in terms of inelegant defining constants ("a metre is the length of the path travelled by light in a vacuum in 1/299 792 458 of a second") and base-10 being inelegant to work with on modern computers.

The whole point of a system of units is that the vast majority of people working with them don't need to deal with the fundamental definitions. For those who do, there's no system that's any less bad than SI anyway (except natural units, but those wouldn't work for day to day things).

It is quite amusing that the old Imperial system of using fractions everywhere is actually more compatible with binary computers (provided the denominators are a power of 2)

Have you ever worked with radians?

Suppose you were teaching radians. Which is an easier explanation of a 90 degree corner. One based on pi, or one based on tau?

The advantage of tau is largely didactic. It helps highschool students a lot more than it does phds.

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