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Well, I've been wrong about things before and I'm sure I will be wrong about 
things again, this has been one of those times. Thanks for the correction.

gl
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On Fri, 1/15/16, David Pike  wrote:

 Subject: [NavList] Re: Great Circle Sailing Chart
 To: garylapook@pacbell.net
 Date: Friday, January 15, 2016, 7:22 AM
 
 For
 practical navigation just place your plotter's straight
 edge on the straight line of the GC on the gnomic chart and
 read out the course against the closest meridian to the
 departure. Then slide the plotter along and read the courses
 at other meridians. Just like reading the course on standard
 flight charts. glYou can’t always do
 that on a gnomonic chart Gary.  The example doesn’t look too bad, because the eye
 is taken to the centre of the chart, which is also the
 tangent of contact, but the lack of orthagonality gets worse
 the closer you get to the edges of the chart. 
 Look in the SW
 corner.  Where would you sit your Douglas protractor?  In the sectors 360-090 and 180-270,
 ninety degrees indicated on the chart is clearly less than
 ninety degrees on a protractor, and in the sectors 090-180
 and 270-360 is more than ninety degrees measured with a
 protractor.  I.e. the chart isn’t conformal, and the normal
 techniques of chartwork can’t always be
 used. 
 
 Just to add to my earlier
 comments, which were written in haste well after my normal
 bedtime.  Gnomonic charts aren’t just used to plan
 navigation trips, although Lindbergh used one to
 plan his Atlantic flight very
 effectively.  They can be used for any activity which involves
 great circles.  E.g. pointing directional aerials or pinpointing
 seismic activity.  For navigational use, the lack of orthogonality
 means that angles aren’t preserved, shape isn’t
 preserved, and scale alters at different rates in different
 directions.  By way of a contrast, the Mercator chart is
 conformal.  Although scale changes, it does so at the same rate
 in each direction so shape is preserved at the expense of
 the chart not being equal area.  E,g.  On some Mercators,
 Greenland appears nearly as big as Africa.  DaveP
 
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