Don’t worry – it’s not rocket science. You choose a notevalue – say, 4n (by convention, that’s what most people would use) and assume that it’s the base for timing differences. If a quarter note is 1.0, then the rate object would have to be running at .5 (one-half the speed) to traverse the distance for a half note or double the rate to traverse the distance for an 8th note, etc. You just get out your calculator and run the numbers….