I wish to respond to Paul Hickley's invitation in his article on “Great Circle Versus Rhumb Line Cross-Track Distance at Mid-Longitude” in the May 2004 Journal of Navigation. It seemed an ideal teaser for an erstwhile Maps and Charts lecturer, albeit 45 years ago, to play with on his 81st birthday last week! Since it was a question for pilots, did not require knowledge of spherical trig, and was answerable in 2 minutes and 12 seconds I thought, as did Paul, that there must be a fairly simple solution. Mine follows.
