Christ, I wonder how some people get through the day! I’m 64 this year, I use inches, feet, yards, miles, millimetres, centimetres, metres and kilometres, depending on which is most appropriate at the time.
Considering to get a centimetre measurement from a millimetre measurement you divide by ten, or just knock the last digit off, it beggars belief that there are people who seem to be unable to grasp a measurement system that is divisible by ten, or a hundred, or a thousand.
Oh, and a foot is about 30.5cm, an inch is 25.4mm, a yard a bit less than a metre, it’s a piece of piss to do a (very) rough conversion.