+% Critical Chance from Rage

[BlackVegetable]

Hey, does anyone know the specifics on the bonus chance to crit from having Rage idle? I'm pretty sure I've seen a loading screen tell me as much and I've noticed it from experience as well.

Is the +% Crit a function of raw rage or a function of rage/maxrage?

How much of a bonus is it?

Is any +% Crit a percentage bonus of existing chance, or is each point 1/100 more than the base critical chance? (that is, if I've got an archer with 10% critical chance and he has some effect giving him +30% does that mean he now has 13% or 40%?)

And finally, do any of you find yourself holding back or holding off on expending rage to secure more critical hits for your troops?

Thanks for the answers!