I'm using the Garmin Rally XC200 for four weeks now. I calibrate the pedals before every ride. I do it as the last step before starting to ride, when I'm already outside.
On Monday I rode the same route as the first time using the pedals a month ago. I could compare the power on the same segments, in very similar conditions. At the same speed and over the same time the pedals measured 65-80 watts less than four weeks ago.
Here's some data from one of Strava's segments on the route:
I'm starting to have doubts about the reliability of the measurement. Any advice?