NavList:

Hello David

You have found the same thing I did.  The phrase "harbor marker" does not appear in a recognized nautical reference.  You and I have both found the reference that Eamonn's note provided.  To wit, "most harbor masters cannot locate their harbor's marker"  with respect to rating a chronometer.

[link deleted]

Brad

I didn’t find that page, so well done Brad for finding it.  Things are starting to make sense.  First looks suggest many similarities to the Wikipedia entry for Celestial Navigation.  Let’s just leave it at that for the moment.  We’re shortly off to Norfolk (UK) for a few days in the hope, amongst other things, of finding some non light polluted skies. DaveP