Measurement - Imperial v Metric

Just seen this thread. I learnt both imperial and metric at school and was fortunate in that just after leaving school, we had just adopted SI units to replace the old imperial ones. Well, in engineering at least. Calculations are certainly easier. Even today, you have to be able to work in both systems. There is still a lot of stuff about that's imperial, e.g. 3/4" pipe, BSF or BSW threads etc. When designing PCB layouts on a computer, one is constantly switching between the two. Most new components are now metric, but the standard pitch for PTH chips is on a 0.1" grid. That's because of the influence of the USA in the electronics industry. I instinctively use inches for estimating small widths, e.g. "that's about 6 inches", but am happy to say 150mm or 15cm. When it comes to property, many floor plans state areas in m^2, which I quickly convert to sq ft, since £/sq ft is the industry standard. As stated earlier on this thread, unnecessary confusion abounds, and has done for many years in this country: all road sign distances in miles; car makers quoting consumption in l/km; petrol only sold in litres, whereas most of us compare mpg figures; beer from pumps sold in pints still, but you can only buy bottles of anything in cc or litres; and so on ad nauseam. You couldn't make it up. It's another example of the powers that be, central government, "expert" bodies/institutions or whatever not knowing what they're doing. I think the use of imperial units in English idiom will be around for a long time, e.g. "the sun's over the yardarm", "give her an inch and she'll take a yard", "my car has been half-inched", "can't fit a quart into a pint pot", "mind your Ps and Qs"...

And there are other examples of imperial rule: pilots always talk of "cruising at 40,000 feet", not km; horseracing distances in miles and furlongs; horse heights in hands; crickets pitches in chains (22 yds.); snooker and billiard table sizes always quoted in ft. and inches...

I can't add anything new or witty about units but I enjoy reflecting on my own metrology journey. It started with the imperial FPS system in O level Physics and A level Applied Maths. A level Physics saw a continuation of FPS and the beginning of the metric CGS system. A Physics degree in the late 60s was pretty much all CGS. During teacher training 70/71 the approved metric system switched from CGS to MKS. Fortunately my 40 years as a Physics teacher saw relatively little further change as the SI system if units was bedded down in 1971. So what do all these initials stand for I hear you ask. Well, FPS stands for the foot, pound, second system with force measured in poundals, energy in foot-poundals and power in foot-poundals/second (with 550 foot-poundals/second = 1 horsepower!!). The CGS system was based on the centimetre, gram and second. Force was now measured in dynes, energy in ergs and power in erg/second. For many purposes these units were rather small hence the introduction of the MKS system with the length and mass units being a metre and kilogram respectively. Now force was measured in newtons, energy in joules and power in watts (if any of you are still awake you might like to know 746 watt = 1 horsepower!) In the world of science we have done pretty well to maintain basically the same set of units for nearly 50 years. Does it matter you may say - actually probably not for most people but it doesn't half come in useful when watching University Challenge. There is nearly always a "Units" question!

I worked for over 40 years at Meggitt [formerly Dunlop] in Holbrook Lane and I had to attend regular meetings to approve & ensure that our technical drawings were internationally correct [alterations were expensive any very time consuming]. All dimensions had to be quoted in both Metric & Imperial. It surprised me that many draughtsmen did not appreciate that Metric dimensions were separated by a comma [i.e. 5,7 mm] whereas UK and US dimensions [Imperial] were separated by a full stop [i.e. 5.700"].

Back in the early 70s I hadn't been back home to Keighley in God's own country for about 6 months for various reasons. On my subsequent visit, the first thing that struck me as I drove into town was that ALL the road signs in the town and on the outskirts now denoted the distances to the nearby villages and towns in kilometres. The signs were still in the same positions at the roadside, but everyone had been altered to the metric system. It was no longer 3 miles to Haworth and the Bronte Country, Bradford wasn't 10 miles away anymore; they were respectively 4.9 km and 16.1km while Hebden Bridge was not five and a half miles away as it had been on my last visit to see my parents but 8.9km 'ower t'ill'. The whole thing took on the appearance of a huge local April Fool joke, except it was July and wasn't funny - it was obvious the town planner in charge of such things didn't come from Yorkshire. He was probably a Lancastrian? A large amount of local finance must have been wasted in the process. When I went for my cross country runs from my parents' house the 'local April Fool joke' turned into farce. I noticed every single distance on every single footpath sign that I ran past had been metricised. The local town planner had entered the realms of fantasyland because each new distance was denoted to TWO decimal places - Hainworth was no longer three quarters of a mile across the fields from Hainworth Shay but was 1.21km away. The pleasant summer evening mile and a quarter stroll up the hill to The Guide pub on the moor top had metamorphosed into a continental 2.01km. And best of all.... to walk from Haworth Worth Valley railway station to the parsonage in the village where the Brontes had lived was not 750 yards anymore but had become 668 metres, even the conversion was wrong!!! But derision and sarcasm of the local population soon won the day as another dollop of council money was spent on demetrification or unmetrification. I do not know which of the two words the town planner would have chosen to use in his resignation letter?

It does have its amusing side. Many years ago, a large agricultural vehicle showroom in Derbyshire ordered a nice new, expensive illuminated sign to go on their new showroom, an impressive brick building. However, when it arrived, it was considerably longer than the intended building elevation! So it had to be sent back. The boss of the firm commissioned was an old Yorkshireman, working well past retirement age, who was used to feet and inches. He was familiar with an 8 foot sheet, not 2400mm. So he converted all the measurements into feet and inches, where he did all his calculations, then on the final manufacture drawing, converted his calculations back into metric. Obviously, something had gone wrong in his calculations! Do you remember the story in the papers, years ago, about the April fool's joke at some local council? It was about the time metric was coming in. An "official" notice went round that time was going to be metrified. The second would stay the same, but there would now be 10 metric seconds in the new metric minute, 10 metric minutes in the new metric hour and so on. Several employees took in seriously and were alarmed that they would lose out on their holiday entitlement now that the week would consist of 10 metric days!

In photography we have a system where 4 equals half of 2.8 and 8 is a quarter of 4. One can have a situation where a 50mm lens and a 150mm lens have roughly the same angle of view - they need to be fitted to different format cameras.

It was quite simple,12 pennies to the shilling, 8 furlongs to the mile, twenty is a score, twenty-five a pony, bulls-eye fifty, ton one-hundred, monkey five hundred, eight ounces to a half-pound, one bean and a bean, a bean and half and half a bean = four beans, Sally's your Aunt Brenda, and Bob's your Uncle, a bob's a shilling, ten bob's half a pound, eight ounces to the pound, four quarts are a gallon, a bushel eight gallons, a quire twenty-five sheets. Could go on. No worries.

What could be easier?

Looks like you've got it "nailed".

When SI units were first introduced they were supposed to increase in thousands. This worked well for most of them but it meant that the units for distance/length were millimeters, meters and kilometers. Centimeters were not supposed to be used, but this made the numbers for shortish lengths unwieldy and difficult to measure with the millimeter being so small, plus centimeters were also in everyday usage, so eventually centimeters were allowed as a "permitted unit". A fine example of the practicalities of an idea not being thought through.

OL, you're right about "not being thought through". The small distance signs we now have on the edges of our motorways are expressed in km, and spaced every 500m. That ties in nicely with the main road signs, where all distances are given in miles. I'm sure everyone who can drive can immediately convert by 0.62137119 in their heads as they drive along at 70mph. Sorry, I meant 112.6540804 km/h. And the irony? The official nomenclature for the distance signs in km is "chainage"; after the imperial chain, 22yds of course. Ain't it simple?

That's right. I tend to use cm, as well as mm, m, km etc. The cm is about the only metric unit I use not based in multiples of a thousand. Everything else in engineering uses thousands or thousandths. So going up it's kilo, mega, giga.. and going the other way, milli, micro, nano, pico etc.

I'm of the perpetually confused generation, never grasping metric or imperial properly. However I'm a master at finding tools that do my thinking for me. I judge petrol by - full tank - or fractions of a full tank. My car will tell me miles remaining to an empty tank, mpg, etc. For calculations metric is a no brainer. Thankfully Google has a nifty conversion tool where you can convert back and forth between all sorts of units eg yards to inches, inches to metres, cm to feet, pounds to kilograms etc. I think of people heights in feet and inches but building height in metres, people weight in stones and pounds but objects in kilograms, long distances in miles but short ones in metres, a pint is a big glass but most liquids I think of in litres. For money I'm 100% decimal.

It's mostly when cooking that I get confused Helen, some recipes sometimes change from metric to imperial. Usually if I am using a recipe I have been using for years I still do it in imperial, victoria sponge would be in ounces. I do admit that when I first started work and was trained as a comptometer operator things would have been so much easier if we had been metric. I would not have had to learn all the decimals for currency to do multiplications. I still convert back sometimes like thinking a second class stamp is now 12s 2