A. All GPS units from all manufacturers have a design positional accuracy of 15 meters.

The GPS satellites are owned and controlled by the U.S. Department of Defense (DOD) and this agency has the prerogative to degrade the accuracy of the GPS signal available to non-military users for purposes of national defense. This is done by what is called "Selective Availability" (commonly known as "SA"). SA is normally turned "on."

SA allows the U.S. DOD to degrade the accuracy of non-military GPS system by as much as +/- 100 meters. At the present time the accuracy of all commercial GPS receivers can vary Between 15 to 100 meters depending on the level of degradation being imposed by the U.S. DOD.

SA introduces a positional error which changes over a period of time. It is not unusual for your unit to show fluctuations in position and speed. This is normal when SA is on.