1581-1626

English mathematician and instrument maker who designed many instruments to simplify astronomical, nautical, and surveying calculations. These include a portable quadrant and forerunner of the modern slide rule known as "Gunter's Line." He also introduced the terms "cosine" and "cotangent." Variations in magnetic declination—the acute angle between magnetic and true north—were first observed by Gunter in 1622, but he attributed the effect to errors. Henry Gellibrand later realized the effect was real (1633).