Software for Cyclists
Join Date: Dec 2003
Location: Redding, California
Bikes: Trek 5200, Specialized MTB
It sounds like it recorded miles, but displayed km (20 km = 12.43 miles).
I've seen this before, especially in the Polar .hrm files. Even though the watch unit is set to display miles, the .hrm file sometimes contains km, and vice versa.
I've not seen this documented anywhere, but I have seen it often enough in some of my customer's .hrm files. The problem seems rare, but it does happe from time to time.
You might want to contact Polar and ask them about it.
While you were riding, was speed, distance, and time being displayed? And, was the exercise time correct?