Technically you can't calibrate a PT. "Zeroing" it confirms that coasting = zero watts. Most newer PTs do this automatically so you don't have to worry about it.
Depends on the head unit and the PM. On my Quarq I put the pedals flat (think 9:00 and 3:00). Not sure if this is needed or where I heard this, but I do it consistently. Then on the Garmin 500 go to the "Ant+ Power" screen. There is an option to "calibrate". Hit that button and let it work. Don't touch the crank. In a few seconds it will give you a value. That value should be relatively consistent all the time. Mine is general +/- 25. Then, when I the road, I can re-zero anytime I want by pedaling backward three times.
On the Powertap, the exercise at start-up is the same except no need to worry about pedal position. Just leave the bike still after you hit the calibrate feature on the Garmin 500. There is also no backpedal option with a power tap.
Depending on the PM I am using, I do one of these little rituals before every ride. It takes 30 seconds while I put on my gloves and buckle my helmet strap. Not sure on the procedure for other head units, but the Garmin 910 works similarly.
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Technically you can't calibrate a PT. "Zeroing" it confirms that coasting = zero watts. Most newer PTs do this automatically so you don't have to worry about it.
On the Powertap, the exercise at start-up is the same except no need to worry about pedal position. Just leave the bike still after you hit the calibrate feature on the Garmin 500. There is also no backpedal option with a power tap.
Depending on the PM I am using, I do one of these little rituals before every ride. It takes 30 seconds while I put on my gloves and buckle my helmet strap. Not sure on the procedure for other head units, but the Garmin 910 works similarly.