Hi Jo,
If you open the file in Nav-View, you have the option to ignore the data that does not have GPS data, or you can go into the file and delete the non-GPS-data, you will see the picture that I have attached. Then you get a continuous count from 0.00. In the box above the data you get the timestamp when it begins and the exact coordinates that you could copy into Google Maps and see where you were when the GPS started to response. That is the knowledge that I have from the GPS-system.
I hope this helps,
Gerhard