Critical hit ability is the ability to do additional damage. The formula for this is:
For non-SIB,
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For SIB,
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,
where
}{(hitLvlMaxed - hitLvlRec)})
The effect of CHA on you critical hits is believed to be linear. At a CHA of 0 the number of critical hits you do is 1%, and when your CHA is 10 you do 2% critical hits.