Garmin GPSMAP 640 - Manual (Page 48)

42 GPSMAP 620 and GPSMAP 640 Owner’s Manual
Marine Mode: Advanced Configuration
Setting System Alarms
From the Home screen, touch Configure > Alarms > System .
Clock—set an alarm using the system (GPS) clock. The unit must
be on for the clock alarm to work.
GpS Accuracy—set an alarm to sound when the GPS location
accuracy falls outside the specified value.
Setting Sonar Alarms
From the Home screen, touch Configure > Alarms > Sonar .
Shallow Water/Deep Water—set an alarm to sound when the
depth according to a NMEA 0183 water-depth sensor is less than or
greater than the specified value.
Water temp—set an alarm to sound when temperature received
via a NMEA 0183 sensor reports a temperature that is 2°F (1.1°C)
above or below the specified temperature.
Configuring My Boat
From the Home screen, touch Configure > My Boat .
Keel offset—offset the surface reading for the depth of a keel,
making it possible to measure depth from the bottom of the keel
instead of from the transducer location. Enter a positive number to
offset for a keel. Enter a negative number to compensate for a large
vessel that may draw several feet of water.
To adjust the Keel Offset:
1. From the Home screen, touch Configure > My Boat > Keel
Offset .
2. Use the on-screen keyboard to specify the offset.
• If you are measuring down to the keel (transducer installed
at the water line), enter a (+) positive number.
• If you are measuring up to the water line (transducer
installed on the keel), enter a (-) negative number.
3. Touch Done to accept the number.