Originally Posted by
kindath
Because as I said, the T in this situation is last CHANCE for the trinket to proc. As in, last autoattack, last special attack, last dot tick, last whatever. Take Bloodlust charm, with 3 base RPPM, and say you have 10% haste and are only autoattacking a combat dummy every 2s. The chance to proc is 3(ppm) * 1.10(haste) * 2(time since last chance) / 60 (sec per min) = 11% chance to proc on EACH hit. It does not care if it's proc'd yet (unless it's on ICD). Then, over the course of a minute, you'd attack the dummy 30 times (at one attack every 2s) and your expected number of procs is 3.3, which happens to be 3PPM + 10% extra procs from haste.
Say you're spamming AOE and hitting a bunch of targets every second, let's say 0.1 seconds in between combat events that can proc the trinket. The chance to proc is 3(ppm) * 1.10(haste) * 0.1(time since last chance) / 60 (sec per min) = 0.55% chance per hit to proc. With 0.1 seconds between attacks, you'd have 600 chances to proc the trinket per minute, and 600 * 0.55% is the expected 3.3 PPM.
The reason it caps at 10s between chances to proc is because if it wasn't, and before combat you spend say 2 minutes buffing up, the formula would be (3ppm*1.1*120s)/60 = 660% chance to proc, aka the trinket would always proc on the first hit. As it is, it's capped at 10s, which makes it (3ppm*1.1*10s)/60 = 55% chance to proc on the first hit, and then say you follow up with an instant 1s later, the chance to proc on that hit goes back down to (3ppm*1.1*1s)/60 = 5.5%.