While trying to figure out the math for Hungering Arrow, we discovered that we don't know how the Devouring Arrow rune works:
Hungering Arrow: Fire a magically imbued arrow that seeks out targets for 115% weapon damage and has a 35% chance to pierce through targets.
Devouring Arrow: Each consecutive pierce increases the damage of the arrow by 70%.
Does this mean that each hit gets another 70% weapon damage added (so a second hit would be 115 + 70 = 185%)? Or that the total damage is increased by 70% (so a second hit would be 115% * 1.70 = 195%)? Or something else? This doesn't make a big difference on the first hit but the cumulative effect could be large.