Polar S625X speed calibration

I've been looking for a straightforward explanation of the speed calibration feature on my Polar S625X. I finally found one here.

"Once you have an accurately measured place to calibrate your S625X, run that distance and make note of the distance recorded by the S625X. Your calibration factor would be

((Actual distance)/(Measured distance)) x 1000 = Calibration factor

or if you have previously calibrated your S625X, the your calibration factor would be

((Actual distance)/(Measured distance)) x (Prior calibration factor) = Calibration factor"