The Sight Reduction Tables for Air Navigation (Pub 249) are published in three volumes. Volume 1, used by both marine and air navigator, contains the altitude and azimuth values of seven selected starts for the complete ranges of latitude and hour angle of Aries. These seven starts represent the best selection for observation at any given position and time, and provide the date for presetting instruments before observation and for sight reduction afterwards. Volumes 2 and 3 cover latitudes 0°-40° and 39°-89° respectively and are primarily used by the air navigator in conjunction with observations of celestial bodies to calculate the geographic position of the observer.