I don’t have any head unit like Garmin or Powertap Joule when purchased the P1pedals last month. I’m thinking that Powertap mobile App can do the job for setting the crank arm length and calibrate the pedal initially. I do know that Zwift cant do anything to the pedal setting. But once the pedal installed then I notice the mobile App can only READ the crank arm length but not change it. Only can update the FW if there have new version.
Then I purchased Powertap Joule GPS+ as head unit to set the crank arm length and calibration. Pairing with Zwift is a breeze using ANT+ and not BLE because Zwift will read as one Left and one Right. In order for Zwift to measure the power correctly ANT+ protocol been using since the manufacturer paired the right to left.
During the ride I compare the power reading in Zwift and Powertap Joule GPS+ and the discrepancy around 3 to 6 watts provided I pedalled at even force. So far P1 and Zwift are friendly matched on my setup.
As an alternative to having the head unit I can also use PerfPRO to change the crank arm length and initial calibration.