Select Settings > System > GPS.

Skyview

Shows the relative position of GPS satellites in the sky.

WAAS/EGNOS

Turns on or off WAAS (in North America) or EGNOS (in Europe), which can provide more-accurate GPS position information. When using WAAS or EGNOS, the device may take longer to acquire satellites.

Speed Filter

Averages the speed of your vessel over a short period of time for smoother speed values.

Source

Allows you to select the preferred source for GPS.