Hi, I can give you the definite answer based on the Greenfoot source code. This is accurate for 2.1.2 and probably most recent versions, but is not guaranteed to stay the same in future. Below is a list of speed setting on the left (which is 1 to 100 as kiarocks said), and the aimed-for frames-per-second on the right. If your scenario cannot sustain the desired FPS (which is almost guaranteed at the highest speeds), it will just run as fast as possible. Here's the list: I've just given every fifth value, but hopefully you get the rough idea. It pretty much doubles the desired FPS every five frames.

Wow, so at the far right (100) it's doing (or attempting to) do 40 thousand frames per second? Jesus. :L Alright, was just wondering because I was thinking of making myself a better way of timing where you could actually input a seconds value and with some calculations it would... well never mind, I can't be asked dealing with that atm >.< Thanks though, that was interesting.