One degree (shown in red) and 89 degrees (shown in blue)
|Unit system||Non-SI accepted unit|
|Symbol||° or deg|
|1 ° in ...||... is equal to ...|
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. Some ancient calendars, for example the Persian 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.
- HP 48G Series – User's Guide (UG) (8 ed.). Hewlett-Packard. December 1994 . HP 00048-90126, (00048-90104). Retrieved 2015-09-06.
- HP 50g graphing calculator user's guide (UG) (1 ed.). Hewlett-Packard. 2006-04-01. HP F2229AA-90006. Retrieved 2015-10-10.
- HP Prime Graphing Calculator User Guide (UG) (PDF) (1 ed.). Hewlett-Packard Development Company, L.P. October 2014. HP 788996-001. Retrieved 2015-10-13.
- Bureau International des Poid et Mesures (2006). "The International System of Units (SI)" (8 ed.). Archived from the original on 2009-10-01.
- "Degree". MathWorld.
- Jeans, James Hopwood (1947). The Growth of Physical Science. p. 7.
- Murnaghan, Francis Dominic (1946). Analytic Geometry. p. 2.