Book excerpt: The sextant is the treasured navigational device of generations of seamen and airmen. It enables position to be determined with good accuracy for ocean navigation, and it was the combination of sextant and chronometer that allowed safe navigation of the oceans for generations of seafarers. Despite the accuracy and ease of use of electronic navigation systems, every navigator should be able to use a sextant. It could even save your life in the event of electronics failure. This book describes how a sextant works, provides practical tips and advice on using it, explains how to read as well as take sights, how to make adjustments and correct errors, and finally advises on how to handle and care for the instrument. Book jacket.