At school we studied in imperial units and I was trained as an engineer in the Royal Navy and all the engineering training was done using SI units.

My first draft to a submarine was a bit of a shock, some pressure gauges were in Bar (1B=14.5 psi roughly) and some were in PSI. Some equipment was made using metric threads for nuts and bolts other equipment was measured in imperial units, so you needed two sets of spanners to have a full tool kit (provided some nice shipmate did not half-inch them).

Subsequent submarines were more metricised but we still kept depth in feet and not metres, we also measured our speed in knots not KPH or even MPH.

On a flight now most in flight displays will give you altitude in Feet and Meters and speed in KPH or Knots.

My last boat did not have 'bar' as a pressure unit but was fully SI and used Pascals as the pressure unit. 1,000,000, Pascals = 1 Bar, so all the guages had a XX x 10^6 monicker and lots of red and green lines to warn us when a pressure or a level was in a danger area.

I now find it harder to think in imperial units as all my work is now done in SI units. The only thing I dont have to think about is a pint, long may that continue.

The Chinese and the Japanese have there own unit of length but this is only used in traditional craftwork and by fewer people. Their engineering is all done in SI units. I drive here using KPH and I swaer metrically (needs 10 shouts of w******'s to attract the attention of the offending motorist).

'Give them and inch and they take a yard' does not roll off the tongue in metric. There wold have to be arguments about whther to use 'Give them a millimetre...' or 'Give them a centimetre....'

I was once working on a project here on depth measurement on a river was going to be displayed in mH20 (metres of water 1mH2=100 Kpa= 1 bar) Quite easy. In the US there are three imperial level units (Inches H20) because three different temperature levels are specified to define the unit. Therefore metric is easier to use.

It is also far easier to do engineering calulations in SI units without making a mistake than imperial units.