Seems to use some units of measurement that are unheard of in my part of the world. Oh 1 inch = 2.54 cm.
Every country in the world uses it except for the US, Burma, and Liberia.
It certainly doesn't dictate what hobbyists will use for a project. Though what does surprise me is that even people with an interest in science don't recognise the benefits of metric. Mathematical formulas often use metric values for simplicity. No doubt you could adapt them for customary values though it would needlessly add complexity thus increasing chances of error.
Wow, I'm surprised how much my original post got modded down. Didn't realise how sensitive US people were about their units.