Item Proce mechanic and formula
 

I am trying to come up with a relatively catch-all formula to compute the DPS value of any trinket/weapon/whatever with a proc chance effect:

((average cast time of spells in rotation * chance to proc)/fight duration) *(effect of proc)/(proc duration + internal cooldown)

is what I have so far. I realize that I might be missing something, but I'm basically using the "chance on spellcast to increase spellpower by X" mechanic to start with. Chance on crit and other such effects should be easily adjustable once I can get the basic formula down.

I think it would look something like this:

How many casts to proc:
(100)/(Proc Chance)

How long it takes to proc:
(Average cast time)*(100)/(Proc Chance)

How much time between procs:
(Average cast time)*(100)/(Proc Chance)+(Internal Cooldown)

Percentage of Time that the Proc is Active:
(Proc Duration)/[(Average cast time)*(100)/(Proc Chance)+(Internal Cooldown)]

Average +Spell Power Value:
(Proc Duration)/[(Average cast time)*(100)/(Proc Chance)+(Internal Cooldown)]*(Proc Spell Power)

You can replace the words "Spell Power" with anything you like, Crit Rating, Haste Rating, etc.

I'm trying to calculate the AP average from [Mirror of Truth]
Please can you help me with that ? :S

EDIT: for a Rogue, so no Average cast time on the formula

(10)/[(Average cast time)*(100)/(10)+(45)]*(1000) <--- ¿?

There's a reasonable discussion of this in the TTT; take a look at http://elitistjerks.com/f47/t21822-proc_mechanics/. If there's anything missing/confusing, let me know and I'll update accordingly.

Thanks for the answer but I can't see that thread, Idk why but the link show me this:

Warning: mysqli_query() [function.mysqli-query]: (HY000/2013): Lost connection to MySQL server during query in /includes/class_core.php on line 1075
The Elitist Jerks database has encountered a problem.

That, or never charge any page :(

Yeah, that page seems... intermittent in it's functionality. I had to reload it a few times to get it to work earlier, and I'm having trouble again now. I'll talk to the admins about it.

For items with 45 second internal cooldowns and 15% proc rate a fair approximation is to assume it procs about 1/minute, or perhaps a bit faster. This in my case anyway matches what I see in WWS parses for uptime of the buff for Sundial vs total time recorded.

The napkin-math theory goes like this.

What you've got is 45+(function based on how fast you cast/% chance to proc) = average seconds between procs.

With a 15% proc rate it takes betwen 4-5 castings to get a 50% chance of proccing.

If you cast ~3 second spells/effects then you're looking at 57-60 seconds, if you cast ~1.5 second spells/effects you're looking at 51-52.5 seconds for a 50% chance to proc. You'll never get 100% chance to proc the way statistics works most of the curve for a typical rotation, including haste and other crap speeding individual casts will get the median proc time a bit under 15 seconds. How far depends on your rotation and how the day went.

A 10% proc rate would widen the gap, probably more like "a bit over a minute" rather than "a bit under a minute". The fixed 45s cooldown keeps these trinkets fairly predictable for long term dps.

Items like mirror of truth that proc on crit obviously depend on your crit rate and are going to be more variable than items like Sundial that proc on hit. Blizzard seems to compensate for that somewhat with higher proc rates after cooldown, at least according to wowhead comments. I have yet to get such an item to play with it myself.