What does Determination really do?

[Nutz]

Like the other secondary stats, the question you ask implies that it's a linear relation (but it isn't). E.g. look at skill speed. Let's say (it's pretty accurate in this example) that 10 point of skill speed decreases AA delay and GCD by .01. Then by adding 100, we've only decrease to 2.4, which is 2.5/2.4=4% increase. Adding another 100 on top of that decreases it to 2.3, BUT this doesn't increase dps by 4% (like the first 100) the new dps increase is 2.5/2.3=8.7%. And while will doubled stat investment, we've more than double the change to dps. So in other words, when dealing with secondary stats you can't assume a linear formula.

This is more or less right except that SS has no effect on AA delay, however, SS returns are nearly linear for practical purposes. As you can see the effect is very close to linear when adding 200 skill speed. In fact, the numbers stay pretty close to linear until you add about 2000 skill speed (going from 1900 skill speed to 2000 is a 20% increase, while going from 2000 to 2100 is a 25% increase). In any case, this is about determination, which acts much differently than skill speed.

Determination has been difficult to quantify exactly. Current formulas have determination adding .11 damage/determination for auto attacks (or about 1 damage every 9 determination) and .035 damage/determination for weapon skills (or about 1 damage every 28.5 determination). This is not entirely accurate, but it's close and can give you an idea of how determination affects damage dealt. If determination has multiplicative affects with main stat and/ or weapon damage in regards to damage dealt it's currently too slight to notice.

For healing, determination is much trickier (or perhaps in the actual formula the game uses it's not, but with testing that's been done and formulas created to match the results it is). Here is a fairly accurate representation of the cure I healing formula for a level 50 WHM. It is not the real formula, but it is over 99% accurate for stat levels that can currently be achieved:

Average HP Healed On L50 WHM = (Potency/300) x [((0.0114xMND + 0.00145xDTR + 0.3736) x Magic Damage) + (0.21xMND) + (0.11xDTR) + (0.00011316xMNDxDTR)]

As you can see, when healing determination seems to add the flat .11 hp healed per point as well as having a small multiplicative effect with both magic damage from your weapon and mind.

The above information came from here and is not my own work. It's all very interesting if you're into that sort of thing.