• Waypoint entry – a position or destination where you enter the Lat and Long. The GPS gives you bearing and distance from your present position to the Waypoint
• Routes – a series of several Waypoints
• Man Overboard or Mark – fix at time of MOB
• Position: - Latitude, Longitude and Time
• Speed Over Ground - SOG (compare with log to get tide effect)
• Course over Ground – COG (True or Magnetic)
• Bearing (T or M) to Waypoint
• Distance to Waypoint
• Time to Waypoint
• Cross Track Error (XTE) in Miles – how far off the selected track route you are
• Charts

In Use:

• Plot Lat and Long on chart – maintain log book every hour. 
• Back up with another source if possible
• Draw a GPS web on the chart for fast boats 
• Find Waypoints from chart, almanac etc. Don’t enter the exact position. Check entry for bearing and distance on chart. 
• Use a compass rose as a waypoint for plotting position
• Find Course to Steer – GPS cannot do this, you may sail on a curve.

Possible Errors:

• Aerial Position - should be low, around the stern rail, not up the mast.
• Aerial failure. 
• Battery failure.
• Datum entry – WGS84 is usual
• User input on waypoint
• Mobile phones signals.