The cadence number displayed on a spin bike is probably accurate. However, compared to a road bike, the cadence number is not the same, since a spin bike has a flywheel and is in effect a fixie on the flat. I usually figure a cadence shown on a spin bike is 10 rpm higher than the equivalent spinning effort on a road bike. I can hit 150 easily on a spin bike, but have trouble getting over 135 on a road bike. Of course watts, speed, distance, and calories are also only useful for comparison between spin bike sessions.