The Metric System

as a machinist by trade in Canada, I still deal with inches vs millimeters, and actually most of the engineers and consulting firms we deal with at work submit drawings to me in the shop in inches. I can quickly conceptualize a tolerance of .0002 as tight quicker than .005 mm, same a 16 or a 32 microinch surface finish, and so on. All of my measuring equipment is in imperial.

I guess it comes down to conception