Any idea why a GPS-Results @500 speed differs from what the uploaded track reflects here? I uploaded a session showing an @500 of 26.989 kts, yet the uploaded speed shows only 22.59 kts. The difference is just a bit too big for me to believe ....

From my experience this is usually due to the signal being lost at sometime in the 500m run.

If you check the datapoints file, usually find at least one data point missing and then the analysis program won't accept the run as valid.

Even with a GW-60 gps, Mike?


Please forward your track to and we will take a look. Could be caused by settings in your local GPS Results Software. On the GPS website also GPS Results is used for uploading, so this could not be the issue. When the filter settings are right both local & server results must be ok is our experience..... 

Will do, thanks. I have now tested 4 separate tracks, all show 2-4 knts difference when uploaded.


I have sent my tracklog but have not yet had a response. I used GPS Tracklog to upload, so can't see how the result could change so radically.

I normally use GT31 but I had a GW52  until it cooked (5 Hz) and same problem if a data point  was lost.

I use GPSAR for datapoint info.

GPSAR normally shows the alpha run with error included. Post to GPSSS and alpha is zero.

Latest was an alpha shown at 20.3 kts with error. Actual clean best alpha was 18.09kts.


Mike, I find it highly unlikely that data points are lost so consistently over three uploaded sessions. I checked each file and can't see anything untoward in the data points. I checked each log file first in GPS-Results, noted the numbers, then uploaded. The uploaded alpha speeds were consistently 2-4 knots under the stated results in GPS-Results. It is almost as if there is a built-in rule in the GPSS algorithm that determines the eventual (lower) speed attained.

Hi Jaco,

When did you send the files ? We haven’t received any tracks till now....