Here are some data from a recent calibration session from October 2017. I was running at a local community college on a well-maintained track.
During the session, Stryd was recorded with a Polar M400 (bluetooth) and Garmin Fenix 3 (ant+) while running in the number 4 lane, which has a standard distance of 423 meters.
Results: My footpod measured about 0.88% short on the Fenix 3 and about 0.45% short on the M400. As a result, a calibration factor of 100.8 was applied to the Fenix 3 and the M400 calibration factor was left at 100.0. You can see the raw and corrected data below. Note that laps were taken at one side of the track with the M400 and at the opposite side of the track with the Fenix 3.