Draw a ray, the center point is aligned with the ray endpoint, the zero scale line is aligned with the ray (two in one), the scale point corresponding to the protractor is aligned, the point is connected with the ray endpoint, and then the degree of the angle is marked.

Angle is a mathematical concept. Used to describe the size of an angle, that is, the amount by which either of two intersecting lines must rotate when overlapping with another intersecting line. Degree is a unit to measure the size of an angle, and the symbol is 0.

The unit of angle is degree, which is the unit to measure the size of angle, and the symbol is 0. A fillet is divided into 360 equal parts, and each part is defined as 1 degree. The number 360 is used for rounded corners because it is easily divisible. 360 has 22 real factors besides 1 and itself, including 2 to 10 except 7, so many special angles are integers.

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In practical application, the angle of an integer is accurate enough. When more accurate angle values are needed, such as measuring the longitude and latitude of a star or the earth in astronomy, in addition to decimals, angles can be subdivided into angular minutes and angular seconds: 1 degree is 60 minutes, and 1 is 60 seconds. For example, 40.1875 = 4011'15 ".

In order to be more accurate, the angular seconds are expressed in decimals without adding units. Degree is the most commonly used unit, and other units are related to specific industry requirements.

In geometry, an angle is a geometric object composed of two rays with a common endpoint. These two rays are called the edges of an angle, and their common endpoint is called the vertex of the angle. The general angle is assumed to be in Euclidean plane, but it can also be defined in Euclidean geometry. Angle is widely used in geometry and trigonometry.

Euclid, the father of geometry, once defined an angle as the relative inclination of two non-parallel straight lines in a plane. Proclos thinks that angle may be a trait, a quantifiable quantity, or a relationship. Oldham thinks that an angle is a deviation from a straight line, and Cabus of Antioch thinks that an angle is a space between two intersecting straight lines. Euclid thinks that an angle is a relationship, but its definitions of right angle, acute angle and obtuse angle are quantitative.