Let's say a crit hit is 100dmg. You have no other sources of crit dmg bonus except byakko's haidate. Crit dmg is now 104, or a 4% increase. Now let's say you have a bonus 16 from impetus, crit damage is 116 before haidate. Adding Byakko's would increase that dmg from 116>120 or a 3.45% dmg increase for crits.
