Funny story on the good ol' metric system. I work on lots of Fed jobs where it is required. Show an imperial measurement on a drawing and the Feds have a coniption.
Drawings come in with metal pipe listed in metric. There is no such thing! A colleague from Russia who worked in metric over there for years before he escaped said that even over there they use imperial measurements for pipe size.
Metric is not used for some things even where metric has always been the standard. If you want to communicate with the US Govt. about a 4" Schedule 40 pipe, you have to convert to an imaginary measurement of 101.6mm Schedule 40 pipe (which can be found on no pipe chart anywhere in the world). If you needed to talk with the Kremlin about the same pipe, it would be a 4" Sch 40.
Not only did we go metric, we make up an non-existant metric system to fit the DC boneheads regulations!