Digital readings

I used to teach management, and large company figures are huge. To help students visualise billions I used to have a little quiz.

If you have £1Billion in cash and stick it under he bed. Starting on 1st January year zero, each morning you get out of bed, take £1000 from the pile and go out and spend it. When did/do you run out of money?

The answer surprises most people and helped students understand just how many £ there are in a billion.

Its about 6th November 2737 - so another 717 years and a few days to go!

I'm mixed like others. Small measurements are millimeters, medium sized ones are imperial and very large ones are metric. the medium sized ones (yards, miles, kilometers, meters) get blurry and a bit confusing.

For engineering, I've chosen to be entirely metric which can be a drawback when sourcing designs.

What I hate about metric though is that there is no 'thou'. My level of precision is roughly around a thou. Actually, with my big mill it's roughly around 0.01mm (on a good day and with a following wind). But I find it easy to say, 'parallel within about 2 thou', but saying 'parallel within about 0.05mm' sounds uncomfortable.

Accordingly, I often post both in threads and might say something like, 'I faced the piece to 10mm and was within about 1 thou'. Which is silly really.

Could we not have a term for 0.01mm? A Cent? than I can say that 'I faced the piece to 10mm and was within about 3 cents' which doesn't mix scales...

(Steve - sorry if I've just booby trapped your thread, but it's sort of relevant).

Iain

At school I was originally taught physics using CGS (centimetre gram second) with units such as erg and dyne and then we changed to MKS and this then changed to SI units so I am glad I am still using the same imperial units that I have used all my life.

Richard

Well with all these interesting comments. I understand what most are saying. Back when messing with the motorbikes, we would literally be able to look at a spark plug or the ignition points & have a pretty good idea of the gap in thou's.

I know when i am doing joinery work i stick to metric.

Yes i am the same as many by having a sense of a thou. If it is say 0.06mm then it's over to the wall chart to compare with imperial.

There are guys like Ade on Ades workshop who many a time will say a size he reads off in imp & then just come out with the metric equivalent size. I don't think in my late years this will happen to me.

I have never been good at numbers though. Back in my college days, doing electrical calculations drove me nuts. Slide rule, alogrithm tables & all.

Strange though how familiarity baines. Like when i was pricing electrical work for a client. They would often want to know the cost inc VAT. I got to a point where i could tell them the price & then how much with VAT added. All in my head. I was never far off the mark. Guess it's when you do something often it sticks. If asked the same question now i would have no idea.

Steve.

The bottom one I can visualise the size, the top only after a mental calculation to approximate an imperial size ! I do use the metric system for some carpentry -- why? well my saw bench has a metric scale so its easier to use millimetres ! For all, well 99% of engineering I use imperial because thats what I was brought up with and all my tools many from apprentice days are imperial, same with all my machines except one lathe.

I used to import a fair amount of product from Italy and of course it was all metric, often we would be discussing size, tolerance etc -- metric tolerance in microns, very confusing to me so asked them to send me a list of the terms used thus with a quick 0.03937 calculation to convert.

Metric Micron 0.001mm

0.001

1 millimetre = 0.03937"

0.1 decimo = 0.00397"

0.01 centesimo = 0.00039"

0.001 micron = 0.000039"

I found this useful, 1mm is fairly easy at 40 thou but when it get down to 1/100 or 1/1000 it is not easy to visualise.

Stevie - just remember that 1mm is about 40 thou - so 0.1 mm is about 4 thou and 0.01 mm is about 0.4 thou - always in a ratio of 1 to 40 (near enough for most things).

If you ever get a bit confused (and sometimes I have to write things down just to make sure they 'look right' ) - then just write " 001.0 mm" and " 0040.0 thou " down, then as you move the decimal point left (or right) just be sure to move it the same amount for both numbers.

0.06mm is six times 0.01mm, so it is also therefore six times 0.4 thou - so it's about 2.4 thou....

(I've just checked and it's really 2.36 thou but you will have to forgive me the difference! )

Regards,

IanT

Edited By IanT on 22/10/2020 15:48:13

Thanks for that. Noted.

Steve.

Yes, that's much easier than training your brain to be equally accurate in both 'systems'**

** well, one of them is a system, the other is a mess.

I use mainly imperial sizes on my old motorcycles but all my machinery is metric. I have both metric and imperial measuring tools but really do prefer to use an imperial depth micrometer.

Lucas distributors were 15 thou, which happened to be the thickness of a fag packet, simples.

DIY likewise metric.

And yes when someone starts ranting about his mill not being any good because it's 0.05mm out I haven't a clue either.

I sometimes get to make stuff to a drawing supplied by one of the other museum volunteers. Metric or imperial, I don't mind which, but fractions are a pain, having to be turned into a usable form.

I think I've posted this link on here before, but still worth a read.

Barleycorns anyone.

http://metricationmatters.com/docs/WhichInch.pdf

Bill

Having watched many, many engineering videos on YouTube uploaded by American machinists like, for example, Joe Pie, Adam Booth or Keith Fenner, I've noticed that they almost always quote dimensions in thousandths of an inch, so 5/8" = 0.625 or 625 thousandths, so if they want to reduce something to, say, 1/2", they know they have to remove 125 thousandths. The clever bit is converting fractions to decimals; I have to consult a Zeus book to know that 29/64 is 0.453" whereas they just know it. I suppose working with these numbers all day every day they just commit them to memory. However I use the technique for Metric - !mm = 1,000 microns, so for example, if I need to reduce a diameter of 22mm to 21,3 mm, 700 microns needs to come off, 350 microns of radius which is equal to 14 graduations on the cross-slide dial. (one graduation = 0,025 mm, 25 microns). Works for me.

I suppose the centimetre is taught as something a bit easier to visualise than the millimetre, and frankly the cm is a bit more useful than the mm for everyday use like clothes sizes and household DIY - but the ISO seems to have become dominated by the ivory-towered who don't think beyond arithmetical nicety.

Everyday use is why units like the inch evolved - they may be eccentric and mathematically incoherent but were based on real people using tools, goods, buildings, clothes etc made to suit human sizes; rather than quantum physics and abstract sums.

We of course know the millimetre as between the diameters of a No.60 and 61 drill....

'

Brought up on Imperial and £.s.d. (and vaguely recalling the principles of Compound Multiplication thereof); working in various engineering and science related trades including having to understand logarithmic units, and with a workshop of machines with thous on them...., I can work in either but find some SI units rather baffling.

I know the Newton is a unit of force but can't disentangle the sense from measurements like 70 N/cm, as labelled on a small motor and worm-gear unit here on my computer desk - I have no idea if I can use this motor for the basis of a milling-machine power-feed because I cannot "picture" 70N/cm.

I recall a college lecturer saying 1N is roughly the weight of 4 apples....

As for the cm.... Yes, the rag-trade and some teachers like it, but I recall a Design & Technology teacher telling me of his frustrating at having to teach his pupils mm because his colleagues who should teach it, won't. I stumble with the centimetre, and often find myself mentally converting it to mm. So if someone tells me something is, "about 15cm by 20cm", I think, "Eh? Oh, 150mm by 200mm. About six inches by eight!"

I have been building a hefty timber bench; and found myself working in both inches and mm, but my 4"-scale steam-wagon's prototype was made to feet and inches and so is the model. Though it seems unsure whether it wants BSF/BSW fasteners or M-series - and of course BA is a metric range!

'

If you really want an utter tangle of ISO-approved units, try this, a real example. The value is negative so the hyphen is a minus sign, but at least it does not expand the Pascal to its kg & m components:

-211.5 decibels referred to 1Volt per micro-Pascal,

.... but it's all right because we can abbreviate it, to -211.5 dB re 1Volt per µPa....

... and be glad the powers-that-be graciously allow us to measure our boilers in Bar.litre not Pa.litre, even if we tend to go and write it as Bar/litre - a division!

(1 Bar = 100 000Pa = 100 000 000 000µPa. At best our ears can or could just detect a sound pressure-level of only 20 - twenty - of those teeny-weeny micro-Pascals).

Yes i always remember mum's 3 year old Viva HA 1964. was 15thou points but i always got better result/ performance when narrowed to 12 thou. Or just a bit more than the Embassy No6 packet. It took me a while to work out that. ( by the way most of my working out is done while laid in bed or sat on the royal throne) Please delete any images.

So mum's Viva. The distributor centre bushing was worn badly. I worked this out because mum said, whenever i go up a hill the car runs terrible, but on the flat it goes great. Also the acceleration is poor. Of course the vacuum advance pulls the points base plate around when going up a hill & accelerating. Causing the base plate to move & alter the points gap. Nothing to do with the thread but i always seem to digress. Sorry. Oh my god i was 15 then. Where have all the years gone.

Steve.

Imperial is only more intuitive if that's what you're used to. Try explaining it to a French or German engineer. Anyone who has done engineering sums involving more than just adding lengths together will surely acknowledge that the consistent units of SI are a lot easier than Imperial with its miriad of conversion factors. Imperial will die out soon whatever the greybeards say, my son designs pharmaceutical robotics, and just doesn't understand inches etc.

SOD tells us that work is mass * distance, no it's not, it's force * distance, and Nigel has a gearbox rated in N/cm, which is nonsense, should be Newtons * cm. Actually torque is the one unit where Imperial has a trifling advantage. It is usual to express torque in ft*lbs and work in lbs*ft, whereas in SI they are both Newtons*m (or mm)

One of the nicer jobs I had in a varied career was driving an articulated lorry, and I well remember a French driver measuring a load to go on the back of his wagon. How did he do it? By pacing out the length and width with one foot in front of the other - in other words in French feet...

I built a sit-in toy car for the grandchildren. It said 'Made In Europe' and 'Printed In Poland' on the box.

I had to open up the holes in the wheels for them to run freely on the axles.

I found the axles were 9,51mm in diameter. No prizes for guessing that Imperial-sized BDS, minus the usual undersize clearance but with thickish zinc plate, was still in use here.

Duncan -

Thankyou for spotting my error.... The label is actually printed Ncm. I'd smply mis-read it.

'

Several years ago I saw the programme for an organ recital in Oslo Cathedral, celebrating its return to service after heavy overhaul. I do not know when Norway went metric, but the instrument's description quoted all the stop names in fus (feet). "Diapason 8fus", etc.

Network Rail appears still to use the Mile, Chain and Yard, and anyway the Statute Mile and Yard are still the only legal standard road-distance units in the UK.

'

Another area where French units have stayed discreetly away seems to be in bell-ringing: a bell is quoted by pitch and weight, or "mass" if you must, but in cwt. & qrs. Good!

Why French units? Invented there! When that country had recovered from its Revolution and the following shambles, it took a grip on its lack of any real system of measures, which varied not only by trade but also regionally.

At least the UK's system was national although there were at one time some trade units like the bushel and a glorious range of beer cask sizes of which the Barrel is only one. The casks' names were defined by standard Imperial Gallons, and anyway the beverages are now packed in only a couple of industry-standard casks and kegs, but as with other things it is a shame when the drive to flatten everything to suit remote bureaucrats and patronise school-children, loses fine old names that hurt no-one and add individuality.

I don't understand though France established the km hence m on a measure of the Earth's circumference as well as could be measured in the 18C, rather than using the Nautical Mile, which I think already existed. The NM, and its derivation the Knot, is directly based on angle of latitude - rather forecasting the Radian!

One thing I deprecate is the American spelling of these French unit names - let us at least respect the etymology despite Webster's Dictionary, so measure metres with meters, leave grams to Mum's Mum, and loiter not on the liter!

Re the ignition points gaps with the engine running better with 12 thou as opposed to 15 thou. Is this not why we started using "Dwell Metre's" ?