Gary wrote:
Larry wrote:
....

Try that with your compass. Chart its error against the GPS headings
over time as you sail and plot it on a line chart. I was amazed how
far off it is. Sure glad we don't use it for NAVIGATION!....(C;

The problem here is the compass heading is the direction the boat is
pointing, the GPS heading is the direction the boat is moving. The two
are always different, always! You can't swing a compass with a typical
GPS. The GPS that give proper heading have two recievers (one at each
end of the boat) and calculate the ships heading based on the different
positions each one gives. There is stille error.

At my helm I have a normal compass (deviation less than 2 degrees, as
near as I can tell), the GPS COG, the autopilot setting, and the
autopilot fluxgate compass. It is rare that even two of these will
agree, and often there are significant differences. I sort of enjoy
this seeming vagueness, but it drives my wife crazy, because she wants
to believe that one is "real" and therefore the others are "wrong"!