Group of four pocket-sized Guidance & Navigation reference handbooks for Apollo and Skylab missions, ranging in size from 3.5 x 4.75 to 4 x 6.75, including: a spiral-bound booklet of "LMS-ISLGC Reference Information, Luminary 173 (1D)" [an unflown revision of Luminary targeted for the Apollo 14 Lunar Module] prepared by General Electric, listing star codes, verb codes, noun codes, alarm codes, flagwords, landing site coordinates, and other guidance and navigation data; an Apollo 15 booklet by Delco Electronics, offering mission summaries and timelines, orbital diagrams, and computer program listings; a spiral-bound booklet of LGC Data Cards for Apollo 17 (Luminary IE) prepared for training use by Delco Electronics, listing basic instructions for the Block II LM Guidance Computer, with listings of verb codes, noun codes, checklist codes, alarm codes, programs, routines, and flagwords; and a spiral-bound Skylab Manual and JDC Index by Delco Electronics, with listings of job description cards for ground equipment supporting the Skylab guidance and navigation systems. In overall fine to very fine condition.