Bruce, yep I thought this might be the case, but didn't have enough info.
I wouldn't be so sure about the mag to true conversion, that could very well be a red herring.
You imply up the page that the radar is using mag mode. Apparently you don't have a fluxgate
compass; so in fact you have no magnetic input into your sytem at all.
My suggestion as a next step is to make sure your entire system is displaying all courses and bearings in true. That way there are no conversions in the system. That should eliminate the mag / true conversion issue, or confirm it.
Have you upgraded the firmware in the plotter? I am not familiar with that model but you can usually upgrade by downloading a fix to a card and booting the plotter with the new card installed in the chart slot.
Is the GPS built into the plotter with an external antenna
; or is the GPS one of the newer Raystar units which has all the brains inside the mushroom? The antenna
will have a coaxial cable output from the mushroom, the Raystar will have a seatalk cable output from the mushroom, and it will also have a LED on it the blinks to tell you various diagnostic information.