You will need

- line;
- the compass.

Instruction

1

*Find the radius*

**of the arc**of a circle. To do this, take a compass and draw a new circle at three points. Point it is advisable to choose are located far enough away from each other, therefore advisable to take the extreme point

**of the arc**and a point approximately in the center. Every two circles must intersect at two points. Swipe through these two points line. Where these two lines intersect is the center

**of the arc**of a circle. The radius is the distance from the center to any point on the circle.

2

Guide segments from the center to the extreme points of the

**arc**. They form an angle, called Central. If possible, measure it. Length**of an arc**in m of degree equal to the product of PI, radius,**arc**and m degrees divided by 180 degrees. pm=π*r*m/180.3

It may be that to measure the angle nothing. In this case, the output angle of the triangle, if possible, or use the formula of Huygens.

4

*Connect the extreme points*

**of the arc**A and B. C Find the midpoint of the segment AB. Note the arc at the middle of m. It lies on the perpendicular drawn to AB through C.

5

Calculate

**the length****of the arc**according to the formula of Huygens, having measured the required values: p≈2k+1/3*(2k-d). Here k=AM d=AB. The formula of Huygens estimated and has an error.