Which weapon?

[Perin]

is that true? ive always read it as .. increases your crit rate, for every spell that dosent crit, increases crit rate. i dont think ive ever seen it last for more than 2 spells.

That's always been my interpretation as well. I've never seen any player testing or clarification from a dev one way or the other though.

I use the AF body, so I'll normally pop excruciate right before thundara. Most of the time it procs on thundaga, but occasionally it will cause a Thundara crit (which I'm ok with since I always pair parsimony with thundaga anyway). Very rarely I've had it still active after thundaga and proc on the following thunder (which sucks).

When I'm not wearing AF body, it's a lot more random. I'll usually use it before Thunder in that case. As long as it doesn't crit on Thunder, I feel it hasn't been wasted. Once or twice I've actually had excruciate time out without forcing a crit at all. That was more than a little annoying.