Agreed, you want to be aware of the differences in power meters, but I would just recommend against using different power meters on different bikes to gauge your training. Even if you use the same power meter on different bikes, I would still expect to see some variance due to drivetrain differences. Instead I think you want to figure out your goal in terms of how much percentage increase in power you are shooting for (e.g. increase FTP +15%). Then, just use the trainer power and stick to it. That way you eliminate the other unnecessary variables, which are just adding more error into the mix.
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