Gunter Scale Rule

Dateearly 20th century

Object number00040058

NameScale rule

MediumBoxwood

DimensionsOverall: 45 x 610 mm, 0.38 kg

ClassificationsTools and equipment

Credit LineANMM Collection Gift from Captain K H Ross

Terms

DescriptionThe Gunter scale rule is an instrument used to facilitate the computation of complex navigational calculations. Invented by Edmund Gunter in 1620, it was a forerunner of the slide-rule (1657) and was used by navigators until about 1900.HistoryThe invention by Edmund Gunter of this scale rule follows naturally from the publication of John Napier's work 'Mirifici Logarithmorum canonis descrptio' in 1614 in which he described his invention of logarithms. Gunter's 'line of numbers' was a line divided logarithmically into unequally spaced intervals from 1 to 10. Each division represented the logarithm of the number inscribed and was proportional to it. Gunter first envisaged his scale as part of the scale inscribed on a cross-staff. However, once augmented by other trigonometric scaled (sines, tangents, chords) a scale of inches and a 'meridian' line for use with charts drawn on Mercator's projection, it was produced as a separate instrument.SignificanceThe Gunter scale exemplifies the technical achievement of mathematicians and instrument makers in the 17th century and is a relatively unusual navigation instrument.