Guild Wars 2

I know they share a cooldown, just wondering what happens to their actual proc chance if you combine them. For instance two superior sigils of air, one on each weapon – will that give me 60% chance of a lightning strike on crit? 51%? Completely indifferent?

from wiki

Sigils that have a chance to trigger on critical hits stack their chance percentages multiplicatively, not additively. For example, two major Sigils of Fire, which each have a 20% chance to trigger on critical hit, will have a 36% chance to trigger, not 40%.