On Thu, 9 Oct 2008 09:01:39 -0700 (PDT), "
wrote:

That might work as a piece-wise approximation.

Sorry, I know that wasn't a very helpful idea. Since a straight line
on a gnomic chart is a great circle if you just count the number of
degrees along the line that should provide naut miles. I'm not sure
how helpful dividers would be in measuring those degrees. I'm also
not sure if they make gnomic charts to a scale appropriate for
plotting such short distances. What would be the point?

Good question since it's so easy to do it computationally. Our
friend Richard Casady claimed he could do it with dividers but I
suspect he hasn't really tried it. The only graphical solution with
dividers that I would have much faith in would be on the surface of a
globe using a taut string. Everything else I can think of would be a
piece-wise approximation using computed way points on a Mercator
chart.