I emailed polar, asking the best way to calibrate. This is his reply:
Thank you for your email.
This is how I calibrate.
Scroll down to Run speed, and press calibrate.
The S625x will then ask about the calibrating distance. I suggest that 1200 meters is minimum but 3-5 km is even better, and that you do calibration of a running track. Start the run calibration, and when you have run 1200 meters, stand on the goal line for 15 seconds in order to let the S625x receive all the information from the foot pod which has a small latency. Press the ok button no matter what the running distance the S625x shows in the display. The S625x and foot pod will now know your running style, and know that you ran 1200 meters when calibrating. The calibration factor will then adjust so that if you go and run 1200 meters again, then the distance showed in the display will most likely be very close to 1200 meters. Once again, stand still on the goal line for 15 seconds to allow the wrist receiver to receive the last data from the foot pod.
So you dont need to change any of the numbes allthough the unit is not showing the correct number while calibrating. The calibrating factor formula will adjust the results.
You are going for a 10000 meters run. The calibration factor which you are given (lets say 1104) is used for your running style. It might be that the watch is actually measuring that you are running 10500 meters, but the calibration formula will automatically adjust the distance. That means that the formula is in one way an error correction which is used in order to get very accurate results. The thing is that there are many different running styles out there, and in order to get accurate results for all the running styles, a good calinration, and a calibration formula is needed.
Why do you have to wait on the goal line for 15 sec? There is a small latency because we want to make sure that all the running data (speed and distance) which the foot sensor is collecting, is send to the S625x wrist receiver.