On Mar 13, 10:58 pm, Bruce in Bangkok wrote:
I also think in real life that it doesn't make any difference. There
you are standing in a moving boat and taking a sight on two fixed
objects. You are just looking for the angle between the two objects.

I don't know how the OP intends to use the compass but 7 degrees is a
lot of error. More than twice what I'd expect from a well corrected
compass. Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS.

-- Tom.