> the SI system (id est, the metric system).

Phew! In my inconfident mind, I was beginning to ask myself whether people were talking of two different systems.

I think that, somewhere in this thread, CGS units hould be mentioned. I'm not sure whether these are a part of the Imperial units or not. They are used in electrodynamics and used the centimetre ("C"), gramme ("G") and second ("S") as base units. When converting to the equivalent SI units, the two factors 4pi and c (speed of light) crop up all over the place, originating in different definitions of certain universal constants. As I understand it, CGS have been the traditional units, but a move towards the SI system is in progress, to the effect that one really has to know two systems. But it works, albeit imperfectly.

jul"that's how smart I am"ian