Comment by hilbert42 | Hacker News Reader

Comment by hilbert42 | Hacker News Reader

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You're right, I should have put 'imperial' in quotes as it's not the same as the British Imperial measurement. You'll note however I did distinguish the French system from the British one by referring to it in lowercase, that was intentional.

The issue came up in a round about way on HN several weeks ago and I should have been more careful here because I wasn't precise enough in my comment then. As I inferred in that post 'imperial' nomenclature is used rather loosely to refer to measurement and coinage/currency as they're often closely linked (in the sense that the 'Crown' once regulated both).

Pre-revolution French coinage used the same 1/12/20 number divisions as did the old English LSD and currencies in other parts of Europe, and that system is often referred to as 'imperial' coinage which likely goes back to Roman Imperial Coinage — but to confuse matters it was decimal.

One can't cover the long historical lineage here except to mention the sign for the Roman [decimal] denarius is 'd' which is also used for the LSD penny, 12 of which make the shilling (£=240d).

So for various reasons both 'old' physical measurement and 'old' coinage are often referred to as (I)imperial. To add to the confusion, modern currencies when converting from LSD/1/12/20 to metric and '1/12… measurement' are often done around the same time. Nomenclature overlaps.

For example, I'm in Australia and the 1966 conversion from LSD to metrified coinage occurred shortly before the metrication of measurement. It was all lumped together as Imperial (note u/c) to Metric (that's how the public perceived it). The Government staged both changeovers close enough so that the reeducation of the citizenry wasn't forgotten by the time the measurement program started.

For the record here's part of length in the old French measurement system:

"Pied du Roi (foot) ≈ 32.48 cm (Slightly longer than an English foot, which is about 30.48 cm.)

Pouce (inch) = 1/12 of a pied ≈ 2.707 cm

Ligne = 1/12 of a pouce ≈ 2.256 mm

Toise ≈ 1.949 metres (A toise is 6 pieds.) <...>"

The other units can be found on the same site: https://interessia.com/medieval-french-measurements/

I think I wasn't clear about the point I was trying to make, because your comment seems unrelated to it.

Pre-metrification there wasn't a French unit system, like we think about those today, where a meter in Paris is the same meter used in Limoges. The actual length of a ligne changed from one region to the next. There was no country wide standard of exactly how much a certain unit is. Such standards were regional, at best, sometimes the regions being as small as a single village.

This is one of the most important results of the French resolution: a consistent system of measurements, regardless of the units chosen for it.

Right. Essentially, before the Enlightenment systems of weights and measures didn't exist in the standardized way we know it today—measurements traceable to national/international standards, etc.

That's not to say local standards—let's call them weights and measures—weren't strictly adhered to and enforced. They were. There are many recorded instances from history to illustrate the point from, say, Archimedes' eureka moment to that of the obsessive and overzealous Issac Newton† when Warden of the Royal Mint was roaming around London checking for clipped coins and bringing the perpetrators to justice.

I'm fiercely pro-metric, and I've had much to say on the matter on HN over the years. So I'm used to the guns coming out from those in the US defending the Imperial system. I've good reason, at school I learned the Imperial system, CGS and MKS (it was before SI). In say physics learning to do things fluently in three different systems was a recipe for mistakes and confusion.

At the risk of repeating myself (link below), learning foot poundals, dynes and Newtons was bad enough but to have to convert between them in exams really was pretty rotten. The other reasons I've also menrioned, I've sat on standards committees and have writtern standards (nothing as illustrious as the ISO but it was for an intergovernmental organization nonetheless). Writing standards is often a tedious thankless task (I don't have to tell you people don't read them for the fun of it).

The link below is me getting worked up on HN over the metric system over a number of rolling posts, and it's not the first. I've referred to it here more for the sake of completeness than anything else. (I don't like rereading my old posts so I don't expect others to do so.)

https://news.ycombinator.com/context?id=43880977

† Newton. Not exactly weights and measures but a well documented case: https://coinsandhistoryfoundation.org/2021/04/30/sir-isaac-n...

The US doesn't use the Imperial system, it uses US customary units.

They're similar but very different.

An Imperial pint is 568 ml; a US pint is 473.

An Imperial hundredweight is 112 lbs. A US hundredweight is 100.

They're similar but very different.

Right. …And that's even worse—the US wasn't even satisfied with the well-established Imperial system and had to mess it up.

Everyone who takes an interest in measurement matters knows the story of the various aircraft that have run out of fuel because the US 'shortchanged' the gallon.

It'd be funny if it wasn't so serious, the last major incident was an Air Canada flight in the 80s.

The rest of the world shakes its head in disbelief.

The Gimli Glider?

Wrong size gallons is a terrible analysis of that incident.

The fueler reported that the density of jet fuel at the time was 1.77, which was in lb/L, since other Air Canada aircraft used lb. Pearson and Quintal both used the density of jet fuel in lb/L without converting to kg/L

In fact, Air Canada was in the process of standardizing their fleet on metric, but failed to carefully train their personnel and failed to establish procedures for accurately transmitting measurements.

Actually, the Imperial system messed itself up, post-1776.

The US did screw up a bit by standardizing on the wine gallon (231 cubic inches) instead of 222 cubic inches. This leads to a fluid ounce that is about 4% larger than an Imperial fluid ounce, and breaks the "a pint's a pound the whole world round" relationship (an Imperial fluid ounce of water weighs an ounce, and a pint of water being 16 fluid ounces is also a pound, which is 16 ounces of weight); in the US, a gallon of water now weighs "a little more" than 8 pounds.

Of course, in the UK, an Imperial gallon of water now weighs exactly 10 pounds. This is because in the 1820s -- which you will note is half a century after the US and UK parted ways -- the UK decided to add more factors of 10 and 7 into their units, and redefined the pint to be 20 fluid ounces instead of 16, and a gallon became 160 instead of 128.

The US and UK systems of measure diverged after 1776, and I'd argue the UK system changed more during standardization and re-standardization from the semi-formal system they shared before.

The meter was also a bit of a gimmick, definitionally -- they wanted a unit that was about three (French/Paris) feet, but a definition that wasn't "my personal yardstick" so everyone would agree to it.

So they played around with various definitions like the 2-second pendulum, until they found one which worked and produced a single indisputable length.

(As opposed to picking something fundamental which was unrelated to previous units. Eg (not that they could have derived it at the time), the hydrogen line, the wavelength of the 1420MHz watering hole frequency, is human scale at about 21cm/8.3 inches, fundamental throughout the universe, and unrelated to previous units.)

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