Gunters Quadrant, 1623-1700.

UNITED KINGDOM - APRIL 11: Made of brass, this horary quadrant has engraved scales to a design conceived by the English mathematician Edmund Gunter (1581-1626) in 1623. The horary quadrant was used for finding local time by sighting either the Sun or a bright star at night. Held vertically, a measurement could be taken from the position on the scale of a moveable bead on the thread of the instrument�s plumb bob. The instrument was derived from the astrolabe and first appeared during Medieval times. Like its predecessor, it includes a two-dimensional depiction of the heavens that is reduced to a quarter. Gunter invented several other measuring instruments which bear his name, and also introduced the words �cosine� and �cotangent� into the language of trigonometry. (Photo by SSPL/Getty Images)