Quarq is available with the DUB bottom bracket. IIRC, about $235 for the left crank arm and spindle with Quarq PM.

Prior to the 18th C., every French village had a steel bar affixed to the outside wall of the local city hall that was used as a standard length. There would be similar standard weights. You could build a building in that village using the local standard length without a problem -- but it was hard to create a market for cut lumber or to negotiate a price for goods in a different village.

That's sort of the situation with most power meters. As long as you're doing things related to training for yourself, you don't need to worry about how different power meters work for anyone else.

A counter-example is when you *do* need to communicate or interact with someone else. Right now, Zwift is having a problem with their elite racing league because inaccuracies in different trainers. There was prize money on the line, and inaccurate trainers meant they had to annul some races.

More broadly, there are uses for power data that don't require accuracy and other uses that do. Certified e-racing is one; measuring differences in rolling or aero drag is another; measuring VO2Max or sprint performance or acceleration are others.

But, as I said above, not many people do those things. Mostly, people just use power data to train, and training yourself isn't a very demanding use. For training, single-sided PMs are fine unless you have some obvious physical problem (like my friend who's left leg had to be amputated).

Pacing (especially on endurance events with lots of climbs) is one of my main uses. Again not very demanding of accuracy in Watts. Also provides a consistent record of my relative riding fitness - at least with the same individual PM.

For competitive Zwifting I’m not at a level where accurate power really matters either. But I can see how that becomes a major issue at elite level.

The calorie formula takes efficiency into account. Usually it is 25% but some software uses a different number up or down. I know that RidewithGPS uses 25% because I can input my average watts and time into a spreadsheet and get the exact same number. This is why you get different counts on different software even though it uses the same input data. I would say though that HR based is wildly inaccurate.

The link below says it is 24% but then uses 25% as the factor. There is wiggle room there but no calculation is going to be perfect anyway, and as they point out if you just use joules (watts x seconds) as a substitute for calories you are close enough anyway since the joules/calorie and the efficiency almost cancel out.

https://www.welovecycling.com/wide/2...d-on-the-bike/