QUOTE(LazyShd @ Dec 25 2013, 12:14)

Trying to calculate auto-cast cost for each spell per turn upkeep. To decide if Innate Arcana worth it for me.
Wiki: Upkeep = casting_MP_cost * Speed of action taken in the last turn / duration
Speed of action taken in the last turn - I do not understand what it means. Explain please.
I have bought IA up to level 4 and I haven't regretted my purchase ever (
note: may not be that good for mages).
Another way to look at it is to look at how many turns you play with it in each arena (or the hardest arena) and see how much mana that adds to. For example if you do roughly 40 turns per round and play 90 rounds, that is 3600 turns. Since the vast majority of those are attacking, you would have have an action speed* of 1.62 (1.08 x 1.5**), so you will save 222.2 (3600/1.62 *0.1) turns of whatever spell you use (because the first level saves you 10%), plus minor convenience as you don't have to cast it. The first level is more about convenience, but when you start to level it up, the saving really adds up, for example when doing PFUDOR DwD (last arena) it takes on the scale of 10000 turns, it adds up to thousands of mana saved, not to mention the awesomeness of not having to buff yourself (as much).
*ignoring the 100 factor for brevity
**I think it appears to be multiplicative, also there appears to be some additional factor because with haste and 30% aspd, i get about 2.15 attacks per stack of buff duration (buff second).
QUOTE(LazyShd @ Dec 25 2013, 12:43)

So if my action was attack with base speed 1 and i have 50% + 8% speed bonus (Haste and attack speed bonus from stats), that means Speed of action taken in the last turn = 0.63 ?
As above it appears to be multiplicative, you might want to add a little bonus as well as it 'appears' to be slightly higher (I would recommend using 1.1*haste if used*attack speed), so try using 1.1*1.5*1.08=1.782 => 0.56 action speed.