Diamond flask Lucky: per cast or per hit?

So the Diamond flask provides your critical strikes with lucky rolls. This means that the critical strike chance is rolled twice and the higher number is picked out. Can anyone confirm if the lucky roll is per cast or per hit?

both

I'll use this thread to state that I still don't get how diamond flasks work. By how much does it increase my chance to crit? Say I have 50% crit chance, how much does a diamond flask help in that case?

To calculate your effective crit chance while using the flask you have to first calculate the chance to not crit.

2 rolls, each having 50% chance to not be a crit:
0.5 * 0.5 = 0.25 => your chance to not roll a crit in either of the two rolls is 25%

Thus your effective chance to score a crit is 75% in this case.

If you have a different crit chance just substitute 0.5 in the formula above, but remember that this is your chance not to crit; with 75% crit chance you would put 0.25 in the formula like below:
0.25 * 0.25 = 0.0625 => 93.75% chance to crit

Cheers

That actually sounds fairly intuitive. Thanks :)

50% crit chance is actually the sweet spot for diamond flask to get the most +% to crit chance.

I love the lucky mechanics, I hope GGG introduces more uniques with it.

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Mark_GGG wrote:

The crit roll for a skill is only made once for each use of the skill, not per hit. Making it roll twice and pick the highest doesn't change when the roll is made.

So if cyclone crits, all way hits would be critical?

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Mark_GGG wrote:

The crit roll for a skill is only made once for each use of the skill, not per hit. Making it roll twice and pick the highest doesn't change when the roll is made.

What about the assassin's mark curse?