The graph below shows the data from tonight's session as recorded on my CompuTrainer (Lab Pro 3D version) and the loan PowerTap. Important points to note are as follows:
- Continental trainer tyre inflated to 110psi.
- CompuTrainer warmed up for 10 minutes at 175W prior to calibration.
- CompuTrainer calibrated after warmup, calibration reading (press on force) 2.37.
- CompuTrainer calibration rechecked after session, calibration reading 2.35 (effectively no drift).
- All power (load) settings controlled by CompuTrainer .erg file, no user interference or adjustment.
Here are the results:
It can be seen that the PowerTap readings were consistently lower, the overall (whole session) averages for the session recorded were CompuTrainer 233W, PowerTap 224W. The average figures for effort 1 were CompuTrainer 265W, PowerTap 257W and for effort 2 CompuTrainer 264W, PowerTap 258W.
So, there was a difference, who knows which figures are "right". If I assume that the ergo function on the CompuTrainer keeps the load steady there did seem to be more minute by minute fluctuation in the PowerTap readings but that's a bit subjective.
Any thoughts on the matter welcomed!