Select Settings > System > GPS.

Skyview

Shows the relative position of GPS satellites in the sky.

GLONASS

Turns on or off GLONASS usage (Russia satellite system). When the system is used in situations with poor sky visibility, this configuration can be used in combination with GPS to provide more accurate position information.

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.