If you have the humminbird asgr-50 gps puck I noticed that for speeds 0-1.5 mph this unit consistently showed speeds approx 0.50 mph higher than my actual speed. As a point of reference I was using the asgr-HA gps puck and the gps in the ipilot. Those two consistently read the same speed. Just an FYI for those that may use that puck.
