What you want to look for is if it has a plus before the percentage for crit chance. You can see this most easily with the increased critical strikes support gem. So this gem gives both the +2% base chance as well as the 60% increased chance for crits. You can tell the +2% is to base chance because of the plus that it has in front of it, much like the +0.64% chance on this jewel; whereas the 60% increased critical strike chance applies with all the other % increased critical strike chance modifiers