My gosh, what a lot of tosh.
After actually consulting a (shorter) Oxford Dictionary:
A rule is a graduated thing for measuring c.f. a slide rule (who ever heard of a slide ruler?)
A ruler is a straight edge for drawing straight lines.
The fact that some things can be used for both purposescreates an ambiguity.
Anyway, if I was Britannia, I'd waive the rules.
Neil