I started using the metric system when I was riding and repairing Honda motorcycles regularly. It's not difficult to learn, but it does take a while to become accustomed to.
Having said that, I still think Carter was a dumbass for trying it, along with mandating the 85-mph speedometer and a 55-mph national speed limit.
Well, I'm familiar with millimeters, due to firearms. I just multiply by 4 to know what it really is.
And meters are just defective oversized yards.
Driving overseas and in Canuckistan, where speed limits and distances are in those stupid kilometers, you just go like hell because no one cares anyway.
If I want liquor, I let someone else mix the drink, so I don't worry about milliliters.
If you don't buy dope, you don't need grams.
That's about it for metrics.