Thread: The invention of Imperial measurement

Well at least by using a chain I can play one or two sports.

And then for added confusion we can ponder degrees, minutes and seconds compared to degrees and their decimal sub units. Oddly, both schemes are used for navigation and military targeting.

I work in nautical miles and feet of altitude which is the international standard except in China and parts of Russia, metres of visibility except in the US where its statute miles and their fractions, knots of wind speed except some places its metres/second. Celsius temperature except for guess where. HectoPascals of pressure except where its pounds/square inch or inches of mercury. Degrees/minutes/seconds except when not.

Almost everything I do in the shop is in millimetres, but for precision work I find thousandths of inches are handy units for what can be achieved reasonably and likely reflect the degree of accuracy I will ever need.

let's not forget the origin of the metre was 1/10,000,000 of the shortest distance between the equator and the north pole assuming a flattening of the earth of 1/334.

A few hundred years ago, in the maritime world, there was a sort of de facto imperial decimal system.

• a nautical mile was equal to one minute of latitude,
• 10 cables equalled a nautical mile,
• 100 fathoms equalled a cable,
• 1,000 fathoms equalled a nautical mile,
• 6 feet to a fathom
• 6,000 feet to the nautical mile.

Easy peasy!

Then it was discovered that the world was a little larger than previously believed. So now:

• a nautical mile is still equal to one minute of latitude,
• 10 cables still equal a nautical mile, and
• there are still 6 feet to the fathom.

But confusingly the current length of a nautical mile is:

• 6,080 feet according to the British Admiralty, and
• 6,080.2 feet according to the US Navy.

Edit: In France, the Mille Nautique is defined as exactly 1,852 metres (~6,076.10 feet). The nautical mile is still used for navigation in the metric countries.

Sounds like you're an aviator! So vertical distances in feet, short horizontal in metres, long horizontal in nautical miles, speed in knots, pressure in hectopascals.

But then we get into measurement of fuel. Here we have US gallons, imperial gallons, litres, pounds, kg - no wonder we continue to have plane crashes caused by fuel exhaustion (AKA too much air in the tanks). And don't even get me started on CofG units for W&B!

I love to retreat to metric units in the workshop - although like you I am occasionally guilty of using thou's when it's convenient.

Metric and Imperial work really well together.
Even NASA uses both (together)
Just look at the Mars Climate Orbiter for example.
Mars Climate Orbiter - Wikipedia

Like when Australia first went Metric, we all got new tapes with Imperial on top and Metric below.
We integrated Metric really fast, with measurements like '6 foot 5 and 14 mill' (mills are much easier to add to inches than fractions)

Originally Posted by Blocklayer

Metric and Imperial work really well together.
Even NASA uses both (together)
Just look at the Mars Climate Orbiter for example.
Mars Climate Orbiter - Wikipedia

It's a nice story to demonstrate a point, except that at the time of the spacecraft loss in 1999, NASA's standards already required SI units (metric). It was a subcontractor who supplied a piece of software against specification which provided output in the incorrect units.

Like when Australia first went Metric, we all got new tapes with Imperial on top and Metric below.
We integrated Metric really fast, with measurements like '6 foot 5 and 14 mill' (mills are much easier to add to inches than fractions)[/QUOTE]

I remember differently.
When we changed tapes were metric only.

Guberment legislation, it was later that Stanley etc was able to sell what we now see everywhere, the mixed tapes which are a pain.

So you mark out to 6 foot 5 inches and then add 14 mm from the other side of the tape?
Just off the top of my head that 14 mm is about 9/16”.
1/2” is 12.7 mm and 1 mm is 40 thou so 1.3 is about 60 thou which every one knows is a 1/16th.
H

Originally Posted by GRK

Sounds like you're an aviator! So vertical distances in feet, short horizontal in metres, long horizontal in nautical miles, speed in knots, pressure in hectopascals.

I love to retreat to metric units in the workshop - although like you I am occasionally guilty of using thou's when it's convenient.

Two systems can happily be used side by side particularly when one system, more often Imperial, is intuitive. I'd see a hard conversion in aviation as introducing a dangerous and potentially fatal period during its introduction, especially in a glider in which you get one shot at landing. We are all trained in visual altitude recognition which helps; but doing mental calculations on final glide or possibly on circuit would present a dangerous change in focus. The sky is a very safe place except right at its edges.

Many were delighted many years ago when the US military went metric given prior "blue on blue" catastrophes.

mick

Aviation is particularly well suited to imperial measurements, sorry to say. The nautical mile reflects exactly what we are doing, crossing lines of latitude and longitude. Airspeed is measured in knots, so windspeed should be too.

Using whole thousand foot increments of altitude neatly captures the actual level of vertical navigation accuracy we can manage. There are 34* different flight levels available using feet, fewer using metric, plus the metric levels are goofy constructs that are almost the same as the the usual flight levels, but they take four times longer to say on the radio.

As far as visibility goes, miles actually work pretty well: 1/2 mile for regular approaches, 1/4 for CAT II, 1/8 for CAT III.

I actually had one of Gough Whitlam's old advisers give me a stern lecture about using imperial measure in my cabin announcement. I gave him the benefit of my thinking on the matter.

Anyway, give ‘em 25.4 mm and they'll take 7.9998 furlongs👨🏼✈️

I work in cardiac angiography.
We use mm for some things such as the size of balloons and stents. 2.5mm to 4mm is the most common range size of your coronary arteries. Of course some are larger and some are smaller, were all different
.018inch .014" .025" .035" and .038", and are common guide wires we use
Catheters are in French scale 4, 5, 6, 7, 8 and so on. The larger the number the larger the catheter
Needles are in different gauges, 25, 23, 21, 19, 16, 14, 12 etc. The smaller the number the larger the needle.

We use all these measurement scales during a case, but you get used to it.

But at home in my shed I'm definitely a mm man.
But I know what feet and inches etc are.

Frank

I just had another thought about mixed measuring scheme:

Pilots set their altimeters to the local pressure, now from a variety of sources, but only a hamdful of years ago it was solely from air traffic control. In North America, barometric pressure is given in inches of mercury, to two decimal places (to? too?). So the pressure is typically 29.92 inches, ranging from maybe 29.20 near a hurricane, to 30.30 under a full moon high pressure system. Naturally those numbers get abbreviated with sloppy radio procedures to “992” etc. No problem, except when those guys fly overseas and get their altimeter setting in hectopascals. 992 hectopascals set as 29.92 inches on the altimeter (they have both scales) means the aircraft will be about 630’ low. I am aware of that happening twice in Melbourne when I was a bystander…but thankfully modern ATC systems pick that up quickly and corrections made. Not so much elsewhere in the world.

The opposite end of the scale - I work in optical fibre/photonics area. Most optical fibre dimensions are in microns (10^-6m), light wavelengths in nanometers (10^-9m), optical filter specs etc. in picometers (10^-12m). It's a rare day I even consider anything bigger than 1.25mm.....sigh.

Standard SM fibre (used in NBN for example) has 125 micron OD (the whole piece of glass), but the light only travels down the middle 10 microns. Not really for people with fat fingers.

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