Damage over Time

DoT = Damage over Time. This refers to effects that deal X damage over Y seconds, rather than (or in addition to) dealing their full damage at once. DoT's are usually some sort of debuff.

Calculations

In Diablo II DoT it was fairly simple, with Poison, Open Wounds, and a few other modifiers and properties dealing X damage every second for Y seconds. The stacking and combination of multiple such effects could be complicated to calculate, but the functions were fairly straight forward.

The mechanic is of much increased importance in Diablo III, and it has many more variables now. For one thing, the "tick rate" of the damage calculation varies depending on numerous factors, such as the attack speed of the weapon used to inflict the damage.

In early beta testing, fans noted that the DoT varied widely, especially for characters dual wielding weapons. In December 2011, Bashiok delivered an informative forum post on the subject, which you can read below:[1]

The tick rate of channeled skills is currently scaled by your weapon speed. This has the side effect of making the resource cost go up, which we’re okay with. It’s consistent with the philosophy that faster speed weapons consume more resource but may do more damage. Channeled skills might still be better with slower weapons though because on a channeled skill, you have as much mobility as you want, so the “mobility” and “overkill” advantages of faster weapons are eroded with channeled abilities, so all you’re left with is increased mana cost for increased damage.

We’ve been thinking of changing the tooltips and going with “ continuously does X% weapon damage”. The reservations we currently have are:

• Even though we say continuously, there’s a pulse rate under the hood, so do players want to know this pulse rate?

• If we did show a pulse rate, we’re adding more complexity to an already complicated tooltip.

However, the benefit of being able to directly compare 135% weapon damage on Disintegrate to X% weapon damage on another skill is super high, so we love that.

This info is all subject to change before and even after release, but it's interesting to get some insight into the more complicated combat mechanics in Diablo III.