This is one of the greatest refinements of celestial navigaton: Weems makes usable the idea of Beij. Each page shows curves of equal altitude for three stars, compensating for the refraction at 5000 feet above Mean Sea Level. Editions beginning in 1940 are larger, on better paper, and show the three stars' curves in different colors. There are two early editions. The first, in 1927, is in mimeographed form--with the sky-blue ink on white paper. From 1928 to 1930 a black-ink on (now discolored) pulp paper edition came out. Star altitude curves were plotted for Harold Gatty's use in navigating around the world in 1931.