Incorrect wattage

Hi. Can anyone help with this wee issue? I’m using an Elite Force mag on the advised setting 3 of 8, Garmin ant+ rear wheel sensor linked to Samsung S8, correct rider weight, wheel size, tyre pressure, refreshed my FTP but my wattage is far too low compared to power produced on a Watt Bike. I can’t say for sure but I think it’s reading maybe 60 or 70w too low. My average is around 120w. My Zwift apps have been installed within the last few weeks. Any ideas what the issue could be? Thanks in advance. Peter

I’m not familiar with watt bike but why do you feel it is the more accurate of your 2 devices?
Can you compare to your out door rides?
If you ride with a friend, which one seems to be closer with a real life ride with your friend.

Hi Tim. That was just an example really. My supposed power output is much lower than friends who I am much stronger than. Watt Bikes are very sophisticated, accurate, expensive static bikes. The search goes on. It’s hard to do a back to back test because my gym is closed and we’re on lockdown obviously. Cheers