MGR reference

With the demise of the player base on the skins network, I've decided to do some shopping around. However, when evaluating RB deals, it's probably a good idea to do some homework to understand how each site determines MGR. Some sites compute MGR by calculating the total rake / number of people dealt in the hand (like skins). I know that there are various ways to calculate a players MGR. Does anyone know of a website or reference that explains MGR on a site by site basis? For example UB and FTP. TIA.