Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - General Additive and Multiplicative Damage Percents

A reddit user called asurreptitiousllama worked it out by creating a weapon in GM mode and then using trial and error to figure out how all the stats increase damage and how they interact.

Devs normally don't show their math. You just have to figure it out using a weapon with the same min/max damage (makes things easier), then hitting a bad dude over and over and recording the damage increase from each stat until you can predict the damage dealt when you just increase your stats to whatever.

In Diablo III, all of the math was figured out by users on the forum, then thrown into google doc spreadsheets.