The Mark IV bubble sextant has a mechanism designed by Lt. Comdr. Ira Hobbs
of the Naval Aircraft Factory that averaged observations along with the times at which they were made. It also has a novel method of illuminating the bubble
designed by Gregory Rylsky, an engineer employed by Pioneer. The form was
introduced in 1941 and remained in use throughout the war.
Ref: Instructions for Operation and Maintenance of Pioneer Instrument
Division of Bendix Aviation Corporation Aircraft Octant FSSC No. 88-0-250 Bureau of Aeronautics, U.S. Navy Mark IV Contract 83600 - March 21, 1941.
Mark 4 Aircraft Octants for Bureau of Aeronautics United States Navy.
Operation and Service Instructions (Teterboro, N.J.: Eclipse-Pioneer
Division of Bendix Aviation Corp, 1943).
I. E. Hobbs, "Octant Time and Altitude Correlating Device," U.S. patent #2,340,324.
Gregory Rylsky, "Illuminating Means for Navigating Instruments," U.S. patent #2,221,152.