Educational ruler

A protractor, comprising:

• a planar disk having a semicircular circumference and labeled in scales along the semicircular circumference;
• a straight line edge connecting two edges of the semicircular circumference;
• a through hole on the planar disk;
• a first edge and a second edge extending from the through hole to the straight line edge;
• a third edge and a fourth edge extending from the semicircular circumference to the straight line edge;
• wherein the first edge of the through hole and the second edge of the through hole intersect at 90 degrees scale of a side of the planar disk to form a first right angle, and an included angle of the first edge of the through hole and the straight line edge of the educational ruler is 45 degrees;
• the third edge of the through hole and the fourth edge of the through hole intersect at 60 degrees scale or 120 degrees scale of the planar disk to form a second right angle, and an included angle of the third edge of the through hole and the straight line edge of the educational ruler is 60 degrees;
• an extension line of the second edge of the educational ruler and an extension line of the fourth edge of the educational ruler intersect;
• an intersection point of the extension line of the second edge of the educational ruler and the extension line of the fourth edge of the educational ruler, and the through hole form a first through hole and a second through hole;
• wherein the first through hole and the second through hole are triangular structures;
• wherein a first acute angle of the first through hole and a second acute angle of the second through hole are located on two ends of the straight line edge, respectively;
• wherein a third acute angle of the first through hole and a fourth acute angle of the second through hole are arc-shaped structures.