[retcore]

Product of the English system here: what are "English numbers"?

I've never seen 0.5 written ".5" going back to Principia.

[loonster]

In the drafting world, inch units are commonly referred to as English. So if things are drafted properly, .500 would be 1/2 an inch and 0.5 would be 1/2 a millimeter.

(Things are rarely drafted according to specs.)