NavList:

Gary you asked: just how do you manage to follow a rhumb line while taking that two minute observation in your airplane?  

You ask the flying pilot to select a magnetically monitored mode on the compass system.  Then, if the system has an Automatic Variation Setting Control Unit (AVSCU), you’ll be flying rhumb lines.  I think I’ve mentioned before, the inside of ours looked like a resin cast of the inside of somebody’s ear rotating with longitude with a little pecker working against it moving in and out with latitude*.   If you don’t have an AVSCU, then you probably have to apply a further correction for change in variation.  As the song says, “Corrections, there are a few, but then again, ……..”.  DaveP
* There was always the danger of an AVSCU run-away, which was another reason for regular heading checks againt the Pilot's E2 Compasses or celestial.