User blog comment:Emptylord/Champion reworks/Sion the Nearly-Headless Axeman/@comment-4068613-20130515162742/@comment-3974211-20130515195334

At 100% health, Hack does 50% bonus damage and Slash does 0% bonus damage. Obviously Hack will damage them, though, so they won't be at 100%. Say you're at 75% health - Hack does 37.75% bonus damage and Slash does 12.5% bonus damage. You're basically guaranteed to do 40-60% bonus damage across the two attacks.