Imperial units of measurement and the future?

I'm really chuffed having changed car recently, mine now says over 800 miles when full. Reassuringly today I noticed it has done 400 miles on half a tank. It's not a small car either. (Note this has been doing in excess of 200 miles per day this week of mostly motorway driving and observing speed limits.)

Sawdust.

 

Nothing to do with decimals: to get the same level of accuracy you just need to quote to the same number of significant figures. So for example, 55 mpg (2 significant figures) is 5.1 l/100km (2 significant figures); but if the decimal point offends, you could express it as 51 l/1000km and it has exactly the same meaning, in a decimal free zone ...

Tom

 

Prejudice is a great time saver..

 

Apropos milk: AFAIK the situation is still (as it certainly was some years ago) that SI units (and a few others based on them) are legally required for many things in the UK but with some specific exceptions. Two of the exceptions are that milk can legally be sold in pints (rather than litres) if it is in bottles; and beer and cider can legally be sold in pints if they are on draft, i.e. not in bottles. I think it is technically illegal for a pub to sell lemonade or shandy by the pint but allowed in practice.

 

If I am driving in Europe and change the settings to KPH rather than MPH the consumtion figures are in l/100km and it all makes sense. It is even good to see the figure dropping.

 

You were arguing accuracy, not usage. It's you who's changing the goalposts.

Simon

 

Certainly - with the French keen to fine on the spot a speedo reading in local currency saves doubt.

 

But you're all missing the point. For the fuel consumption to mean anything in the muddled-up UK it needs to be in litres/mile (or miles/litre) or some variant thereof. Which of course, means mixing up both systems.

 

Absolutely.... and in any case, of all the factors affecting fuel consumption, none include what units the damned stuff is sold in!

 

As a wine bottle is three quarters of a litre and quite nearly one sixth of a modern gallon - that is since the 183os - I have used this as convenient
intermediate to calculate between fills from petrol pumps in litres to miles per gallon, the odometer being in miles.

Railway relevance: the change from 16 to 20 fluid ounces to the pint was due to Davies Gilbert who was asked byTrevithick: what would be the
loss in power of a steam engine running without a condenser? Gilbert said: in principle, one atmosphere/ 15 psi ( as rebranded in our
life times, one "bar"). This caught on thoroughly via Penydarren, "Catch Me Who Can", Puffing Billy, the Rocket etc. to the developed
steam locomotive and traction engine. The notion that a unit of five pints would catch on because with 2o fluid ounces to the pint
there would be 100 fluid ounces in it went nowhere. And quite right too: the future of calculation
with computing has become binary.

 

The purpose of mpg figures is to compare vehicles, trips etc. against one another, so what fuel is sold in is irrelevant.

Sawdust.

 

If you use a spreadsheet (as I do) to keep track of your car's fuel consumption in mpg, you need to include a conversion factor for litres to gallons. But that is a one-off task when setting up the spreadsheet.

 

I think you'll find that inches and feet were used as units of measure in other parts of the world, too, Toplight - after all, before such things as tape measures and rules were invented, what other way would you have of measuring things, other than comparing them to bits of your body?

Horses and ponies are still measured in hands and inches, with one hand being four inches; beer and milk in pints; sheets of plywood are either 8 x 4 feet, or 6 x 4 (regardless of shops marking them in mm!); throughout most of officially metric Europe, their main line railways' track gauge is 4' 8 1/2" - or 5 feet or 5' 3"; and (contrary to what Railboy said) modern industry does NOT only use SI units - every integrated circuit has its legs on 0.1" centres!

There's a lot of rather silly criticism of the multiplicity of units of measurement in the Imperial system, and the difficulty of converting one to another; in reality, I found that once I started work, every job used units which were appropriate to that line of work, so you never had to convert chains to inches - because people like land surveyors (who worked in chains and links) had no need to use inches, and bricklayers who worked in yards, feet and inches never needed to use chains. Similarly, fencers and ditchers used rods, because it was a handy size for them. Compare that with an engineering drawing I saw of a double decker bus, where every dimension was marked on the drawing in millimetres!

And how about the fathom (6 feet)? Dead handy for measuring lengths of rope - hold one end of the rope between finger and thumb, stretch your arms wide and grasp the other end between finger and thumb on the other hand, and you've got a fathom of rope. And not many people know that, in early English, 'fathom' meant to embrace, and was the length a lover could wrap his arms around his beloved! Which is why we still use the word 'fathom' in the sense of grasping something - e.g., "I couldn't fathom it at first, but now I've got it."

And what about drill bits? The old letter and number series drills make perfect sense when you realise that rather than going up in fixed steps, they go up by a steady percentage in size - so if one is a tad too small, you can go to the next drill in the series, and it will be a reasonable amount larger, regardless of whereabouts in the range it is, rather than going up in fixed amounts like 1mm or 0.5mm, which may well be too coarse in the smaller drills, and too small in larger sizes.

And the ultimate irony; I read a bit of a blog written by a bloke who had moved to Provence in France, and called in a few local carpenters and builders to do some repairs and renovations. He was watching them marking out a job one day, looked closer and found they weren't using metric measurements at all. When he asked, it turned out they were still using measurements based on parts of the human body - like the width of a thumb, the distance from fingertips to elbow, and the length of a foot - which were standard units of measure in France before the Metric system was invented!

When the Englishman suggested that they ought to be working in Metric measure, the tradesman looked at him in puzzlement, and said "Pourquoi?"

 

The whole "Integrated circuits use imperial measurements" thing is probably a bit outdated. It certainly used to be true that IC packages had legs at 0.1" pitch - but ICs with that package standard are now a relatively small proportion of the market.

As I said upthread, one of the big problems with non-metric measurement was that many countries used vaguely similar measurements with similar names, but there was no standardisation. For example, Sweden and Ireland both standardised on 3 foot gauge for narrow gauge lines - but in Ireland that was 914mm and in Sweden it was 891mm.

 

"Inch" seems to have varied quite a lot. I read somewhere of some rifles made in USA to drawings supplied by Enfield. The parts were not interchangeable with Enfield built because nobody had told the Americans that the drawing were based on the "Enfield Inch" not the normal Imperial Inch.

My old childhood encyclopaedias listed several different "Mile" measurements.

(Regardless of the still current "Nautical Mile" and almost identical "Sea Mile")

 

As a grand statement, you're correct that it's total rubbish - only DIP packaged ICs are 0.1" pitch, and you're correct they're only a stupidly small proportion of ICs used these days. However the surface mount "SOIC" package is at 0.05" pitch - they're used quite a lot...

...however most of the various "SOP" packages (of which there are many different) are at 0.5mm pitch, SOTs are 0.95mm, which isn't a round number imperial dimension either. 0.65mm pitch is another pitch encountered (0.02559" - almost, not quite!), quad flat packs are often 0.8mm pitch. Once you get to BGA packages the common pitches are 0.5mm , 0.8mm , 1mm. Anyone saying "ICs use imperial" is showing their lack of knowledge of the subject matter.

In terms of connectors you still can encounter quite a few 0.1" pitch parts, but then there are an awful lot of 2mm pitch connectors as well, along with 5mm pitch and a host of others, so not enough to build an argument one way or another. You used to encounter BA threads quite a bit in electronics, although usually they're metric now. Of course B.A. stands for "British Association" and are neither a metric nor an imperial thread system, the diameter starts at 6mm OD and 1mm pitch (so is it metric?) but then each size after that is a geometric progression, so most BA sizes aren't a round number in either metric or imperial (although some come close: 5BA = 0.126", whilst 7BA = 2.5mm), and the pitch is neither a round number in either system either. The thread angle is unique to BA as well, and the profile is different to both metric, imperial or the American interpretations.

To say the electronics industry is ruled by imperial dimensions is rubbish, however it does have a mix of systems. Ultimately they're just numbers, it makes not a blind bit of difference what the system is called. When setting up component cells do you space the pins at 2.54mm, or 0.1"? Sorting boards you'll often order either 0.8mm or 1.6mm thickness, but then choose between 1oz or 2oz copper for it.

Who cares, I was brought up and educated in the metric system. If I'm working on something built to metric dimensions I'll use metric. If I'm working on something built to imperial dimensions I'll use imperial - saying something is 8" long is a lot easier than 203.2mm, but then saying something is 12mm is easier than 0.47244094488188976377952755905512".

If I'm working to my own choice it'll tend to be biased towards imperial, but I'm not afraid to throw something odd in using metric if it happens to be a more convenient figure - they're just numbers representing a distance (or weight, or volume, or pressure...). It ain't the end of the world to swap between. Does your computer run on Unix, Windows, DOS, CPM, Mac OS? Underlying hardware doesn't care, and they all do the same end result. (and it seems you get obsessive fanboys for each of those as you do for measurement systems).