The only PM that has to be calibrated to a rider is the iBike.
Strain guage based PMs are calibrated to a specific amount of force on the strain guages. Weight (rider and bike), gravity, wind resistance, and rolling resistance doesn't need to be known in this type of system. The only thing that needs to be known is that if I place a certain amount of force on the strain guages, the correct amount is displayed on the computer in terms of watts (the actual calibration may use torque).
Last edited by NoRacer; 03-11-09 at 06:03 AM.