Here is the probability table for the standard three-step generation: Say that only 1 Potion of Strength has been generated so far: If an armor is generated (out of crypt, flooded vault and room of traps), it has a 33.831 % probability to be a Leather armor. If you find instead a Scale armor (12.806 %) it has a (13+98+552)/6483 = 10.227 % probability to be cursed.