how is hitting calculated?

[adeyke]

AFAIK, it'd only get +1. The +1 thing occurs when the item is first generated, if it has ED on it (and items either have ED or they don't). If you add ED to it afterwards via sockets (including runewords), it'll already have a base defense and that's what will be used to calculate the new defense.

I will now do some more testing on how the ED from sockets stacks, though.

EDIT

I've confirmed my own calculations in 1.09. Just adding all the EDs (except the ED based on clvl) together gives the correct results.

I modded a unique cuirass (base 188-202 defense or 203 defense if it has ED) to have 50% ED and 3 sockets. I made recipes to spawn this and some Puls (30% ED). After inserting the Puls, I had these results:

0 Puls = 304 defense
1 Pul = 365 defense
2 Puls = 426 defense
3 Puls = 487 defense

These numbers match 203 + floor(203 * (.5 + .3 * numberofpuls)).

They do not match 203 + floor(203 * .5) + numberofpuls * floor(203 * .3). If it did, the values would be as follows:

0 Puls = 304 defense
1 Pul = 364 defense
2 Puls = 424 defense
3 Puls = 484 defense

I conclude that my assessment of all ED sources (except ED based on clvl) simply adding up does match empirical evidence from the game.