How to build a circle without a compass?

The easiest way is to take some kind of round object and circle around the edge. Some people use coins, glass, CD, etc. You can take two pencils and tie with a thread. Put one in the center of the circle, pull the other to the full length of the thread. We hold the first in place, and wrap the second in a circle so that the thread is always taut. It is necessary to leave a mark, so the second pencil should touch the paper. Using a ruler, you can also mark a circle with points. Attaching the zero to the center and rotating.