[DonRotolo]

What you want is a PID loop. Search the term here in Chief Delphi, particularly in the White Papers section.

What a PID loop does is look at the motor's speed, compare it to what you have told it you want as the motor's speed, and increases (or decreases) the motor speed so they match.

You wrote "Very Accurate" but what exactly do you mean? +/- 100 RPM? +/1 1 RPM? As you might guess, these are both pretty accurate, but one takes a lot more effort than the other. Also, if your load is fairly constant, it is a lot easier than if your load varies widely.

You can get tighter control of the motor by making your loop run faster. If you run the loop at 100 times per second, you can maintain better control than if you run it once per second, for example.

If you read the papers and still don't understand, just ask. We love explaining PID.