Comment by cxr | Hacker News Reader

Comment by cxr | Hacker News Reader

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Here's my pitch for encouraging the adoption of metric units in holdout places like the US: acknowledge that the foot is a convenient goldilocks unit for describing "human-scale" objects i.e. those that you are likely to find yourself using your hands to work with, and advocate for the widespread use of an SI-based unit that is neither the centimeter (itself being too small for this purpose) nor the meter (being too large).

The decimeter (i.e. 10cm; ⅒ of a meter) has been hiding in plain sight and fits the bill adequately. It is, however, awkward to communicate. It's about the same width as the width across an average adult's hand, so let's rebrand the decimeter as the "metric hand", or just "hand" in informal contexts.

Conveniently, there are approximately 3 metric hands in 1 foot. The error, 1.6mm per hand, is negligible, and in instances where accuracy and/or precision is at a premium you can rest safe knowing that it really does accumulate at 1.6mm per hand exactly, and not some intractable quantity like the one that comes up with approximating 1 kg as 2.2 lbs.

Previously: <https://news.ycombinator.com/item?id=28455838>

I've had the exact same thoughts about "kilometer" being more difficult to say in English than "mile", and I've heard the term "click" being used for 1km.

I'm not sure if "hand" can catch on anymore; how about maybe "deci", pronounced as "desi"?

As an Australian who's used metric in everyday life, construction, signal aquisition, cooking, etc since ~ 1970

Building work is all millimeters - no decimal points and it scales well for fifteen foot (hah!) long wall units with shelves and doors down to the thickness of a saw cut.

3200mm is 3.2 metres (close to 10 and half feet) and gets thrown about in a work shop as "thirty two hundred".

Working in mm ( mills ) in building and workshops is a single unit solution with no decimal points and no confusion when chalking numbers on a wall or bit of sheetrock | paper | wood, etc - it's all mills.

As for the kilometre, that's pretty formal, mostly it's just 'K' as in "it's about 20 Kay down the road".

"clicks" gets used .. but we're lazy and K is shorter still.

In Sweden, I've pronounced it "dess", which works really well.

Well as a Brit I'm pretty 'bilingual' when it comes to measures. The foot is pretty useful, but you never need the precision.

As you say, it's a human scale measure. If you're getting the tape measure out, just use cm and metres.

> If you're getting the tape measure out, just use cm and metres.

The point is that people who get paid to use tape measures do measure things in feet and inches and aren't "just us[ing]" centimeters and meters instead. The proliferation of the metric hand would help with this, since it sidesteps the downside to centimeters and meters I've described.

Settling on centimeters as a common unit and neglecting the decimeter is quite odd on its own.

How are you defining 'human scale' units?

To me they're units that you can eyeball. Units that don't inherently have to be accurate.

If you want accuracy you can use a different metric. If the newspaper described something in terms of football pitches, that doesn't preclude giving the the actual area also.

So I don't see the problem of keeping the foot (~30cm) and using actual metric for the base.

>Settling on centimeters as a common unit and neglecting the decimeter is quite odd on its own.

Well every industry that that im aware of uses mm over cm. Building material is commonly sold in 2400mm heights, more commonly than even 2.4m and if there's an industry that needed the decimetre surely it's the building industry, but even they went the other way and settled on mm.

> How are you defining 'human scale' units?

"'human-scale' objects i.e. those that you are likely to find yourself using your hands to work with"

And I'd say that it's clear enough from context that what I'm taking about is basically "whatever people in the US use inches and feet for (or a large part of that set, at least)". Again, that's the whole point of this thread—things that people continue to use feet for and how it impacts the adoption (or lack thereof) of metric units.

> If you want accuracy you can use a different metric.

"The point is that people [...] aren't"

> I don't see the problem of keeping the foot (~30cm) and using actual metric for the base.

The foot is not a metric unit, full stop.

> Well every industry that that im aware of uses mm over cm

How tall are you? Is that something you answer by reporting it in millimeters?

You're also ignoring the part about how centimeters are not an opportune unit for the types of things I'm describing due to their scale. That makes millimeters even less so.

>"'human-scale' objects i.e. those that you are likely to find yourself using your hands to work with"

>How tall are you? Is that something you answer by reporting it in millimeters?

I wouldn't describe a human as something I would use my hands to work with.

Anyway if you asked my height I would say 6ft. If I actually measured myself eg for a BMI I would use cm or mm ~180cm ~1800mm neither of those are hard.

I don't really get why you're arguing against me on this. I know both units. Inches and feet are useful for some things, and I use them for the things I find useful.

I could have the opposite discussion with someone who only uses metric, that imperial is useless because it doesn't do X and they can't imagine ever using it until their imagined use case is fixed. Ultimately it's what you're used to. But if you want the human scale units then imperial is there.

Is there a reason why you insist on missing the point (ignoring it, rather)?

As an imperial tape measure user, I hate base 12. I've memorized a number of multiples of 12, but c'mon.

> If you're getting the tape measure out, just use cm and metres.

Or just use millimetres.

This document goes over the arguments for cm versus mm, and generally argues that mm/m/km will work for most situations:

> ◊ 4 core units - metre, litre, gram, and tonne;

> ◊ 2 prefixes using the same conversion factor - milli meaning 1/1000th and kilo meaning 1000 X; and

> ◊ 2 concepts - square metres and cubic metres.

> In Australia metrication has been most successful in the areas where we used millimetres. Metrication programs using millimetres have been fast, smooth, and so economical that many individuals and companies have profited from the change.

> Metric conversion has been least successful where centimetres were chosen as the small unit for everyday use. Metric programs using centimetres have been painfully slow, characterised by bitter internal squabbling, and expensive. Failed attempts at metric conversion all have this one thing in common — they tried to introduce the metric system using centimetres.

* http://www.metricationmatters.com/docs/centimetresORmillimet...

It also keeps things 'clean' with consistent 10^3 jumps (also with g/kg/t(onne), mL/L/cu. m).

> One rather startling fact about the Australian metric conversion is that nearly all of their industries opted for the millimeter as their preferred unit of measure, including the construction industry. The plans for Australian houses are drawn up in millimeters. Why use something as small as a millimeter to design something as large as a house? Because decimal numbers are eliminated from the blueprints. Which means that the guy on the job site running the radial arm saw never has to deal with anything but whole numbers. Which means that he makes fewer mistakes. Which means that waste is greatly reduced.

> Actually, no centi-anything. Also, no deci-anything, no deca-anything, and no hecto-anything. […] Drop these four prefixes, and there are only two remaining that non-technical people will ever have to deal with commonly: kilo for thousands, and milli for thousandths. Conversions between measurements become almost unnecessary, and on the rare occasions when they do crop up, there is one and only one conversion factor to remember: 1000.

* https://themetricmaven.com/naughtins-laws/

If you're (e.g.) a machinist and need smaller, there's µm, another 10^3 jump; if a chemist, mg.

Well yes. In practice mm do tend to be used, even in construction.

Cm will never die out though. Schools (certainly primary) are all cm and m. Plus 1cm3 of water is 1g

Which makes the litre equal to one cubic hand.

Hiding? At least in Sweden it's used all the time. Unless they stopped doing that in the 17 years since I left.

The foot is convenient for more than just human scale things. The speed of light is 1 ft/ns to within 2% and the speed of sound in air is 1 ft/ms to about 12%.

The speed of light is 3×10^8 m/s or 0.3 m/ns (accurate to 0.07%). The speed of sound is 343 m/s at 20°C, or 1 km in 3 seconds (accurate to 3%)

Both of these are just as easy to remember.

ft/ns and ft/ms seem pretty useless to me. I guess they work for room-sized things, but go outside and you're converting to miles anyway.

I have issue with describing the speed of sound or light as human scale.

The simplicity of remembering 1 foot is utterly drowned out by trying to appreciate what a nano second is.

As a factoid it's easier to remember yes. But a factoid in isolation is useless. So unless you're going to do E=MC2 in imperial

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