Determine the radius of the earth with one protractor and three poles

The first is to take two places on the surface of the earth with a distance of at least 100 km,

I took two places here, A and B, at a distance of 160 km. Now the AE poles at point A and the BC poles at point B have to be placed perpendicular to that place. Because point B is perpendicular to the sun, no shadow will fall on this pole, but the shadow of the AE pole (AF) will fall on point A.

The next thing I will do is re-place a pole (AD) at point A so that no shadow falls on point A. So the AD poles and BC poles are parallel, Since they did not create any shadows, now I will determine the angle <DAE between the two AD poles and the AE poles with a protractor, which is a very simple matter.

Since the AD ​​pole and BC pole are parallel, then <DAE = <BOA. Because they are alternate angles, here, <BOA is the angle formed at the center of the earth. Here, the distance between points A and B is 160 km, and the angle of emission at the center is about 1.5.
Thus, at an angle of 360, the distance to the surface of the earth is about 40030.26 km, which is called the circumference of the earth. Now we know that circumference means 2πr.
2πr = 40030.26 km
From here, r = 6371 km is found, which is the radius of the earth.
Eratosthenes: Method.