Limitations of Polar RS 400 SD

I purchased one of these last week. I’ve run the same route 2 days in a row and have questions re: the accuracy limitations.

ASSUMPTION: The unit comes with a standard calibration coefficient. Though I haven’t calibrated it yet, the results should at least be repeatable.

First question…Is my assumption correct?

The run is basically an out and back on a lake front which always has some type of wind. Yesterday’s wind was 15 mph tailwind/headwind. Today was a 5 mph crosswind. The running path has marks approximatly every 1/4 mile. I took splits at each mark.

3/31

With the tailwind, the distance recorded was between .23 and .24 miles. On the return route (headwind), the distance recorded was between .25 and .26 miles. It totalled up as 2.53 out and 2.58 back for a distance of 5.11 miles.

4/1

Once again, it measured longer on the way back than out, even though the wind was less intense with a different direction. 2.67 out and 2.71 back for a total of 5.38 miles.

Identical routes in different conditions with a fairly sigificant difference in total mileage (5.11 vs 5.38). Which one is correct? In a tailwind/headwind situation, does the accelerometer “miscalculate” the actual “force” and provide faulty data?

Has anyone else experienced differences of this magnitude? I’d like to know if I got a bad unit.

TIA.

You have to calibrate the watch. Yes it comes “pre-calibrated” or something along that line, but you have to calibrate it to be able to make accurate assessments.

And remember that the Footpod of the RS400 is not as accurate as that of the RS 800, but that is why one costs twice what the other does.

Bob