I think it is the average #

of people who filing for past old labor monthly. Not sure. It depends on how many people from Mainland china files for PERM each month. It is hard to calculate. Back to several years ago, people from Mainland also needs to wait for their PD current to file for 485, right? What is the pace of PD moving in EB 2 at that time? What is the total # of h1 visa yearly back to those year? Then you can calculate how fast the current PD move. Say if back to then, they gave 180000 h1 b1 per year, the PD moves up 1 every month. Then you can assume it takes 1 month to clear up three months OD for PERM. Don't forget old LC keeps filing as we speak. So you can also fator it into the equation.