"alan_m" wrote in message
...
On 11/01/2019 04:28, wrote:

If they've got to 16 or 18 without realising there are imperial
measurements, I doubt they're about to get any knowledge anywhere.

What may be obvious to older contributors on the group may not be so for
someone who has only been educated using metric conventions.

My secondary school and college education 45 years ago was using SI units
which I've continued to use throughout my career. My early experience of
using imperial tools was working on 10 year old cars when I was in my late
teens and later with plumbing with a DIY renovation a house.

The last time I used imperial "in anger" (emphasis on "anger") was when I
was helping my dad fit a new hot water cylinder at their holiday cottage. We
were trying to work out whether the baulks of wood (maybe the eponymous 4x2)
would be strong enough to take its weight. We only had a tape measure
calibrated in inches - and no calculator. I knew that 1 litre of water
weighed a kilogramme or that a gallon of water weighs 10 lb. But how do you
go from measurements of height and circumference in inches to weight of
water?

Not knowing the magic 277 cu in = 1 gallon (= 10 lb) factor (a number I've
now committed to memory!), the easiest way was to convert to centimetres
(using gross approximations like 2 cm to 1 in and pi=3), do the pi R^2 L
calculation, convert to litres (divide by 1000) and hence to kilogrammes.
All we needed was an order of magnitude value - neither of us knew to the
nearest 10 gallons / 10 lb how big and heavy a typical cylinder is.

We obviously estimated correctly the amount of wood needed to support the
cylinder, because it's still there 40 years later.