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# Degree (angle)

 Degree Degree diagram.svg One degree (shown in red) and 89 degrees (shown in blue) Standard: Non-SI accepted unit Quantity: Angle Symbol: °[1][2] Expressed in: 1 °[1][2] = turns 1360 turn radians π180 rad gons 109g
In mathematics, a degree is a common way to measure plane angle. It is written with the symbol $^{\circ}$, where $360^{\circ}$ corresponds to the entire circle.[3][4][5]

It is not an SI unit. The SI uses radian to measure plane angle. However, according to the SI brochure, it is an accepted unit by SI.[6]

## History

The actual reason of choosing the degree as a way to measure plane angle is unknown. One theory says that it is related with the fact that a year is approximately 360 days.[4] Some ancient calendars, for example the Persian calendar and the Babylonian calendar, used 360 days for a year.

Another theory says that the Babylonians divided the circle using the angle of an equilateral triangle. The angle was then divided into 60 parts. This is because they used sexagesimal or base-60 numeral system.[7][8]

## References

1. HP 48G Series – User's Guide (UG) (8 ed.). Hewlett-Packard. December 1994. HP 00048-90126, (00048-90104). Retrieved 2015-09-06.
2. HP 50g graphing calculator user's guide (UG) (1 ed.). Hewlett-Packard. 2006-04-01. HP F2229AA-90006. Retrieved 2015-10-10.
3. "Compendium of Mathematical Symbols" (in en-US). 2020-03-01.
4. Weisstein, Eric W.. "Degree" (in en).
5. Bureau International des Poid et Mesures (2006). The International System of Units (SI) (8 ed.). Archived from the original on 2009-10-01.
6. Murnaghan, Francis Dominic (1946). Analytic Geometry. pp. 2.