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

No, the doubling of single leg power is just an obvious fudge to keep the price down, it probably doesn't matter unless you have a severe imbalance which is likely to change, e.g. recovery from injury. Sure, they're not measuring actual total power, but at least they are measuring actual left leg power and letting you guess what that means for total power.

The problem I see is that it seems to treat the crank as a beam, which gets bent in one plane by pedal force. What actually happens to cranks is that they get bent in two planes and twisted, and the amount of twist changes a lot depending on the eccentricity of the applied load. The crank also stretches or compresses if the load is not precisely tangential to the circle described by the pedal. The 2nd plane bend, twist and stretch will deflect the strain gauges too, and riders with a wider stance will twist their cranks more than riders with narrow stance, for the same applied load. Also, even a particular rider will apply a more eccentric load when they lean the bike while riding out of the saddle. Unless they have been spectacularly clever with the placement of the strain gauges and the algorithm which calculates true circumferential force regardless of eccentricity and atangentiality*, they can only measure true torque for one unique value of eccentricity and tangentiality. In other words, they could make it accurate for a load applied precisely in the centre of the pedal and exactly tangential to the pedal locus by calibrating against a torque measurement at the BB axle, but they can't make it accurate for all riders in all circumstances.

*I just invented that word. It's the angle between the pedal force vector and a tangent to the circle described by the pedal. It has two components, since riders tend to push inwards or outwards as well as applying a force which tends to stretch or compress the crank,

Awesome post. Repped.

Is there a massive job to calibrate for all the different cranks? or am I thinking stress/strain not out'n'out force. Thats kinda why I assumed they made asthetic copies of NDS crank arms.