Critical hit ability is the ability to do additional damage. The formula for this is:
For non-SIB,
![](http://www.codecogs.com/gif.latex?CHA = \sqrt{hitLvl})
For SIB,
![](http://www.codecogs.com/gif.latex?CHA = \sqrt{progressToMaxed} * 10)
,
where
![](http://www.codecogs.com/gif.latex?progressToMaxed = \frac{(hitLvl - hitLvlRec)}{(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.