Raid counter guide data

Does anyone know how the raid counter guides arrive at their DPS and TDO numbers for the raids? I'm trying to do an apples to apples comparison for how SD TTar does compared to Golem (and how Alolan Golem does compared to its Kantonian counterpart) in a battle vs. Ho-oh, but I can't figure out how the guides get their numbers, because I get different numbers when I use GBS (using lvl 40, 15 IVs). Can't find any info on the site that gives their methodology either.