Sextants at Greenwich: A Catalogue of the Mariner's Quadrants, Mariner's Astrolabes, Cross-Staffs, Backstaffs, Octants,

This book describes the history and development of navigating instruments. Before satellites these were used to measure the altitude of the sun and stars above the horizon, to determine the ship's position at sea. The book also contains a catalogue of 347 mariner's astrolabes, cross-staffs, backstaffs, and octants, sextants and artificial horizons.