[Kavious]

This miiight be what your looking for

https://wiki.project1999.com/Game_Me..._Attack_Chance

(% Chance to Double Attack Per Hit) = (Double Attack Skill Level) / ("MaxSkill"*1.05)

The value of "MaxSkill" may be ~400 (unconfirmed). That would mean at 200 double attack skill half of your hits would trigger a double attack.