Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

Can I take a different answer, that maybe doesn't cost me a new powerrtap?

Give Saris a call, they (were, two years ago) a massive pain in the arse to get to answer the phone, but when you get the (seemingly single individual who handles all PowerTap stuff) on the blower he's very clued up.

My understanding is that if the hub doesn't return a calibration value that is a) between 500-525, and b) stable, then it's hosed and requires RTB'ing, although if it's a new one then they may be able to stick a fresh torque tube in it - mine was an SL+, and they didn't have spare parts for them anymore, so I "won" an upgrade to the G3.