# How do similar procs interact?

Tried looking around for an answer to this question but most guides only talk about specific items. On a lot of the loot that I get there are generic procs (`X% chance to XYZ on hit`).

If I have multiple items that have the same generic proc are these all separate rolls or one single roll for that effect? For example, lets say I have 3 items with `x% chance to blind on hit`. A has 1%, B Has 1.5 % and C Has 2.5%. Does this translate into a single roll with 5% chance to blind, or just 3 separate rolls?

• For the specific items you're referencing, are all the chances separate rolls or one single roll? I would expect it to be consistent in general. – Sadly Not May 28 '14 at 22:30
• Can you give an example of two items with same proc? – ykb May 29 '14 at 9:08
• @ykb edited for example clarity – worseone May 30 '14 at 0:26
• @worseone what I meant to ask for, is an example of in-game items that have the same effect proc. I just can't recall any actually sharing one... – ykb May 30 '14 at 7:42
• @ykb: worseone is talking about generic items, with "Chance to Blind on Hit", "Chance to Fear on Hit", etc, as one of their random modifiers, not specific items. – MrLemon May 30 '14 at 7:44

### We might never know.

The only way to know this is by looking at the code. While players are quite crafty with backwards-engineering game mechanics, I highly doubt someone will figure this out, since the difference is just too small notice.

Then again, this means it does not impact gameplay at all.

### How small is it?

According to this list I found on reddit, the maximum proc chance for generic items is 4.5%.

I have written a small Python script that loops over all unique permutations of 3 items with the same proc, ranging from 0 to 4.5 on each item, calculates the difference in chance between `X+Y+Z` (added proc chance) and `1-(1-X)*(1-Y)*(1-Z)` (seperate proc chances), and spits out the maximum difference, as well as the average.

``````M=46 #Python range() does not include the upper bound, uses integers.
a=[]
for i in range(M):
for j in range(i,M):
for k in range(min(1,j),M):
a.append(((i+j+k)/10)-((100-100*(1-i/1000)*(1-j/1000)*(1-k/1000))))
print(max(a),sum(a)/len(a))
``````

The maximum discrepancy is with three items with a chance of 4.5%, and is 0.60%. which means 13.5% proc chance with the additive calculation and 12.9% with the separate calculation.

The average discrepancy is around 0.15%. As I said above, this is too small to notice in regular gameplay. If someone has 3 4.5% items, and has singled out enemies and hit them (optimally with a regular attack) long enough to get statistically large amounts of data, feel free to answer this question.

### Logical conclusion, but pure conjecture on my part

With differences so small as to not impact gameplay, I don't think someone took the effort to program an additive calculation into the game. With a separate calculation, all of these effects can be handled independently and without any crosslinking.

• There are defintely higher rolls possible: Blind Faith or The Sultan of Blinding Sands for example, in a very short test it did not seem/feel like it was stacking... so it could be that the desciption actually is correct `chance to` instead of `chance increased by` for crit for example – DrCopyPaste Jun 6 '14 at 22:01