Sextant

A sextant is a device used to measure the relative angle between two visible objects. It is of use as a navigational aid on Earth, Britannia and Serpent Isle, and may be used to calculate longitude and latitude. Sextants appear in Ultima IV, V, VI, VII, VII Part Two and IX, as well as in Martian Dreams.

Description
The sextant is a tool commonly used in celestial navigation, as it allows its user to take an accurate measurement of a heavenly body relative to the horizon. Once a navigator ascertains this angle, they may use it to reliably determine their geographic position. Such information is invaluable at sea and in uncharted wilderness, as magical means of divining one's position (such as peer gems), are often ineffective in regions void of notable landmarks.

History
Sextants first came into use in Britannia during the Age of Enlightenment, and were originally one of the many specialized goods available only through the Guild of Thieves. During their quest toward Avatarhood, the Stranger would need to learn a special password, "D," to obtain one from the guild's shops, as these clandestine merchants did not advertise sextants' availability to buyers. Later, during the days of the Oppression, the hero could obtain one from David of Greyhaven, who claimed to have invented the device.

By the time of the Gargoyle War, sextants had made their way into Britannia's greater markets, and could be bought from lens workers such as Ephemerides. The instruments became increasingly common pieces of equipment as the world entered the Age of Armageddon, and were eventually available to wayfarers through most reputable shipwrights.

Trivia

 * In reality, a navigator using a sextant to determine latitude and longitude would also need to have access to an almanac giving the locations of the celestial bodies being measured. Depending on the method being used to calculate their position, other devices, such as a marine chronometer and a a set of sight reduction tables to assist in calculations. Otherwise a sextant can only report latitudes, the simplest of which is the noon observation of the sun.
 * Sextants appear in Martian Dreams, where they may be found amongst the supplies brought by Terran explorers to Mars aboard their space cannon.
 * A commemorative golden sextant serves as an emblem of office at Britannia's Observatory.