Pup wrote:
MM is an SI standard, Gugs. It's not just "those countries".
That is doubly incorrect.
The symbol for millimetre is mm. Symbols for units based on a persons name begin with capital letters (A W Pa N ...) The prefixes for factors greater than the basic unit use Upper case (M=mega, G=giga T=tera) but there is a glaring exception in the case of kilo which uses k (K=Kelvin temperature).
The SI unit of length is the metre not the mm which is 1/1000 of the standard unit.
I posted earlier that there is another glaring exception to the SI units. The basic unit for mass is the kilogram. In all other cases a kilo prefix means that it is 1000 of the basic unit. I questioned why a new name had not been applied to this unit. I suggested Archimedes but that would have used A as the symbol which conflicts with Amperes.