yea, if you use the numbers that PT displays (avrage players per table) to calculate the RB you will come somewhat short, because PT rounds down those numbers. And because it's a bad way to calculate it, bound to get it wrong.
rbcalc does it the same way, but instead of stacking the total number of players then dividing them by the total number of games, to get a number like 7.352546252352352, then just chop of the decimals....
It calculates the exact rake for each hand, then stack all the rake together.

Though you can calculate it correct if you make your own sql script I recon, or ripp someone elses. Check the pokertracker forum, or just use rbcalc [img]/images/graemlins/smile.gif[/img]

cheers