I just built up an old bike, and was lucky enough to pick up an older SRM power meter for it. My current team race bike has a different type of power meter on it, dual sided and wireless. The sensors bond onto the crank arms with little pods that transmit to a Garmin or similar computer. A consideration is where exactly do you place those sensors onto the crank arms?
The logic is that there is an optimum placement, or sweetspot. But does that differ between both sides? The spider plays a role in the right side crank stiffness. The left side has fewer factors. If you are off by a millimeter, you get uneven readings. In my case, I have a 58-42% balance consistently. In reality I dont know my true wattage.
Now bring in my "new" SRM. At first I forgot to set the zero offset. So going downhill or pedaling lightly had me putting out zero watts, even with the cranks moving. There should be watts displayed when the crank moves, since there has to be force involved.
I did a few hills on Wednesday. My watts were lower than my race bike. Holding 300 seemed difficult.
So, in understanding data, how we derive it is quite important. It is very difficult to get alternate means of capture to agree.
It will take a while to iron out the issues with both bikes and hopefully I can get similar numbers from both.