How do you know that your trainer reads 9% lower?
Probably because you set up your outside bike on the trainer and compared power output from both?
Are we talking about a wheel-on trainer?
If so, this will sound disapointing but with another bike on your trainer, it is almost 100% sure that power values will be different. That is because power from a wheel-on trainer is very dependent on the bike/trainer interface. Two different bikes have a different position on the trainer and thus the tension off the trainer roller on the tire is different. The tires are different and probably the tire pressure is different. So you can’t simply port the power from one bike to another on these trainers.
If you can temporarely transfer the power meter to your inside bike, you can make it match quite closely. Check this post:
https://forums.trainerday.com/t/power-match-not-working-well-on-shorter-intervals/987/12?u=medtechcd
After doing that, remove your Power Meter and do not recalibrate your trainer!
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