I think Alain has digressed to thoughts of wind in his hair and horsepower under his seat... "Write when you find work!" - is an old expression used by my instructors to recall attention when a student's mind drifted away.

More to your concern, Roy: I think that you will want to pick a sample time that yields results near full scale as at high rotations per hour (RPH), small errors will compound quickly. Perhaps you will consider changing the calculation period over different speed ranges as 0 - 10 MPH, 11 - 25, 25 - 50, 50+ (or some such) so that your results don't follow Alain down the path to fantasy .

Oh, belatedly I see this is Alain's suggestion as well. At least he has not yet disappeared over the horizon.