Not a problem mate, should be useful for other peeps too.
Some stuff which might help shed some light:
I have an instruction manual here next to me which is pretty big, but here is what is written in it:
Circular is exactly the same as Linear, only that it's mainly used with Camera's which cannot Meter exposure correctly. Meaning camera's which are 'divided', refracting, prism or half mirrors.
So basically, same stuff, only used really for certain camera's.