The total amount of ilvl I have is 6010. When this is divided by 12 (omitting the job stone) it comes out to be 500.83. When including the job stone, this is 503.33r(repeating decimal).
Yet the ilvl displays a value of 502.
I suspect the unused shield slot is counted as -1 instead of being part of the division as that would bring down average a lot.
Therefor for jobs that don't use sheilds, it's simply (TotalIlvl / 13) - 1
With 2H weapons it counts your main weapon twice.
It is (total level + level of weapon) / 13.
6010 + 520 = 6530 / 13 = 502.307692308
The job stone isn't factored into the calculation.
Yeah that works.