I've been really liking my Vector 3's recently and swap them between my TT and road bikes frequently. I also have two Quarq DFour power meters (one on each bike) and a PowerTap G3 on my TT bike. I bought the Vectors primarily for travel when I can't bring my bike but my collection of power meters allows me to also do some power comparisons. In general, the Vectors track really well with my other power meters, but when I move them between bikes, there is always a period where they are "off" by 5-10 watts compared to the other power meters-- sometimes they run too high and sometimes they run too low. Nevertheless, that's still up to a 20 watt difference when I've mostly been riding at less than 200 watts! This happens despite manual calibration after each swap. Also recalibrating after a few sprints seems to help (but not cure) the problem. I haven't had any extended rides since I've had them. Also, power changes around quite a bit if I put the washer in or remove it (the axle easily clears the chain without the washer).
So now the questions:
(1) Are there any tips or best practices for doing a manual calibration (e.g. pedals in a specific position)?
(2) Apart from rider safety, should I care about pedal installation torque in terms of accuracy? What about using the washer? Is there a general preference one way or the other in terms of accuracy?
(3) Most importantly, does accuracy improve time? In other words, do the pedal "settle in" over a few hours of riding and "auto zero" begins to make up for smaller calibration differences?
Thanks! All in all, the Vector 3's are a great product and I really like them!
--Ken