2 digit pass score is 75 and three digit pass score is 182 for step 1. Both are equivalent for over all performance. None is percent or percentile or number of questions corrrect. Two digit score is required by some medical boards for licencing purposes.
Three digit score ranges from 140-280. The relation ship between them is that cutoff 75 = cutoff 182. The cutoff 182 is revised from time to time but this always remains equivalent to 75. Ex. in case the three digit score cutoff was increased to 185 then 75=185.
For now 75 = 182. This relationship is linear till the point where 99 = 243. Therefore the three digit score above 243 will always have 99 as two digit score eg. even if you have 280 as three digit score your two digit will remain 99.
Simplest calculation will be to multiply two digit score with 2.4 or 2.45. Ex. 90 X 2.45 = 220. This is true in the linear range of 182 to 243. Above 243 it is totally flat and below 182 i dont know haw far it is linear.
I guess that answers a few questions about the confusion between 2 digit and 3 digit scores.