It is also known as gon, grad, or grade. One grad equals 9⁄10 of a degree or π⁄200 of a radian. In continental Europe, the French term centigrade was in use for one hundredth of a grad, and the term myriograde was in use for one ten-thousandth of a grad. This was one reason for the adoption of the term Celsius to replace centigrade as the name of the temperature scale.
The unit originated in France as the grade, along with the metric system. Due to confusion with existing grad(e) units of northern Europe, the name gon was later adopted, first in those regions, later as the international standard. In German, the unit was formerly also called Neugrad (new degree), likewise Nygrad in Danish and Norwegian (also Gradian), and Nýgráða in Icelandic.
Although attempts at a general introduction were made, the unit was really only adopted in some countries and for specialised areas, like surveying. The French artillery has used the grad for decades. The degree, 1⁄360 of a circle, or the mathematically more convenient radian, 1⁄(2π) of a circle (used in the SI system of units) are generally used instead. In the 1970s and 80s most scientific calculators offered the grad as well as radians and degrees for their trigonometric functions, but in recent years most offer degrees and radians only.
The international standard symbol for this unit today is "gon" (see ISO 31-1). Other symbols used in the past include "gr", "grd", and "g", the last sometimes written as a superscript, similarly to a degree sign: 50g = 45°. "Grad" was commonly used on calculators with LCD displays, as "DEG", "GRAD", and "RAD" could all be represented as a subsection of a panel with the letters "DEGRAD".
Each quadrant is assigned a range of 100 gon, which eases recognition of the four quadrants, as well as arithmetic involving perpendicular or opposite angles.
One advantage of this unit is that right angles are easy to add and subtract in mental arithmetic. If one is traveling on a course of 117 gon (clockwise from due North), say, then the direction from one's left is instantly convertible into 17 gon; while the direction from one's right is 217 gon; and the direction from behind one is 317 gon. A disadvantage is that the common angles of 30° and 60° in geometry must be expressed in fractions (331⁄3 gon and 662⁄3 gon, respectively). Similarly, in one hour (1⁄24 day), Earth rotates by 15° or 162⁄3 gon.
Gradians are also convenient when working with vectors on the complex plane. The exponent of the imaginary unit on any given vector is equal to its angle (argument) in hectogradians (100 gon) from the positive x-axis: has an argument of gradians.
Use in surveying
In surveying, the gradian is the default unit of angles in many parts of the world. Subdivisions of gradian used in surveying are c's (1 c = 0.01 grad) and cc's (1 cc = 0.0001 grad).
Conversion of some common angles
- Angular frequency
- Angular mil (military measurement)
- Harmonic analysis
- Steradian (the "square radian")
- Patrick Bouron (2005). Cartographie: Lecture de Carte. Institut Géographique National. p. 12. Retrieved 2011-07-07.
- Cartographie – lecture de carte – Partie H Quelques exemples à retenir