yeah right now the spell increase doesnt live up to what it says :p thats why most go melee warrior for OP dmg compare to actually a mage

I haven't messed much with Spells yet (I'm only two builds in and neither was spell centric), but I'm getting it works similarly to other damage calculations in the game.

You've got a Damage Value and Percentile Bonus, which is a Sum of ALL applicable. So, if your Damage is 25 and your Percentile Bonus is 100% then your Spell does 50 damage, since 100% more damage is a 2x multiplier.

But here's the catch: the Percentile Bonus is an additive result from ALL applicable Percentile Multipliers. So, take the above scenario and now equip something that boosts your damage by an additional 10%. Your Percentile Bonus goes from 100% to 110%; which means your 2.0x multiplier is now a 2.1x multiplier, which would make your damage 52.5. That's how you go from 50 to (about) 52 with a 10% boost.

Does that make sense?

its simple ...

damage percentage not work on the principle -- dam + 50% + 10% +20% adding every percentage to previous sum
example ( 20 as base dam + 10 = 30 + 3 = 33 + 6.1 = 39.1 ) ....

instead the sum of all percentages together is added to base damage
example --- 80% ( 20 base dam + 16 - 80% = 36 )

so if you adding more and more new percentages basically every new one will add less damage to base ....