Sight reduction tables (HO 229, HO 249)

Sight Reduction Tables are precomputed solutions of the astronomical triangle that turn an assumed position, declination, and local hour angle into the computed altitude Hc and azimuth Zn without trigonometry. NGA Pub 229, formerly HO 229, is the six-volume marine set tabulating to 0.1 arcminute for any declination and latitude. Pub 249, formerly HO 249, is the three-volume air set: Volume 1 carries selected stars for a quick fix, Volumes 2 and 3 cover the Sun, Moon, and planets to 1 arcminute, faster but coarser. The navigator enters with whole-degree assumed latitude and LHA, the reason the assumed longitude is shifted to a whole-degree LHA.