What kind of computer are you developing on? I remember, I had the same issue when working with a laptop computer I used to have. I suspect that it was because the computer automatically v-sync'd itself and so the timing would always come up at/around 59-60 fps, so you might be having the same issue. I guess the best way you could check is to draw one polygon to the screen every frame and see what framerate you get. I assume that you're also not putting any delays in your code that waits for the program to have passed a certain amount of time before drawing the next frame (where you could also possibly get the constant framerate). Anyway, good luck! EDIT: Hmm... I didn't realize someone was posting when I was. But INTERVAL_ONE wasn't the case with my laptop, so I'm not sure.