Dunno, what I do is divide the difference between the FPS the game is meant to run and the FPS the game is running at, this gives me a constant(mathematicaly speaking) of course it's realy a variable. then I just multiply this value with any movement values. The result is a game that will run at the same speed in any machine despite the difference in FPS (of course as long as the PC is capable of running the game at a decent FPS. I'd say 20 FPS would be the minimun specs)