Originally Posted by
Zaskar
As I understand the system I bought - Shimano/Stages L/R power meter - one PM reports to the other and the L/R balance is calculated and reported. The other arm reports power - doubled. The surprise for me (before buying) was that Stages does not take advantage of each PM's data and average them - and report THAT as the power output. That seems like an easy way to get a more accurate total power output. Maybe it's a head-unit thing - Wahoo and Garmin computers are going to do that math? A better Stages App could... maybe?
No, that's not right. Your original impression was correct. The R side reports force to the L, that force is compared to get balance, then the total forces are combined and sent to the head unit. There is no need to double just the left side, and that's not what they do. That said, there are still two issues: the Shimano R side 4-arm crank is known to be a less-than-optimal design for measuring force, and that you have close-to-even balance *on average* doesn't mean it's close-to-even at any particular instant. The Shimano 4-arm crank is actually kind of a problem for this use.