S20 Odometer Accuracy

The odometer on my S20 is grossly inaccurate. I tested carrying both a GPS enabled phone and a Garmin GPS device --- either of those would record in the neighborhood of 5 miles on a particular course. The S20 (reset to 0 at the beginning of the round) reports in the neighborhood of 2.5. At times when I finish a round and I look at my score it shows 25000+.

Is this just a poorly implemented function or is there something I need to do in order to improve the accuracy?

Thanks for any thoughts ...