My attempt to simplify this:Take your total post count, devide it by your posts per day rating. That will give you the number of days you have been registered at SB. Then multiply the number of days you have been at SB by 27 (to account for time at SB) and then add that number to your post count. That gives you your ranking number.
Ignoring your actual post count, what this ranking does is awards you 27 points for every day you have been registered at SB, each post you have is also a point.
post count / posts per day = A;
A x 27 = B;
B + post count = ranking number.
For me, I got 2510.