Quote from Kamui1770
skill and element% damage is factored into the same pool. It may not say on the sheet, but it is. 15% meteor + 15% arcane = 30% bonus. These are additive multipliers. They add up into the same pool and then get multiplied. In game sheet is quite insignificant. It doesn't tell you the effective damage or toughness.
Area Damage is also NOT factored in. because that damage is relative to real time mob density. The only info that is given to you is 20% proc coefficient, 20 yard radius, and your splash damage pool. You can have 20% AD or 150% AD, you will always have a 20% proc rate.
ultimately, you pretty much need excel, a calculator, or D3 planner up all the time or with you if you want to know how much dmg you do or will do.
That is just not true.
meteor% (rolled on items, not a legendary affix) is additive with itself and other skills like for example magic weapon or taeguk gem.
they are additive since they are all in the category "damage increased by skills"
element% is a separate multiplier compared to "damage increased by skills"
so your example would go 15% meteor + 15% arcane = 1,15 x 1,15 = 1,3225 = 32,25% bonus.