What about the two fixed points of the ellipse drawn by the carpenter?

First determine the highest point of an arc, then calculate the radius, and then draw an arc with that radius, starting from the highest point, drawing left and right, and drawing the length on the map, or first determine the length of the arc, mark two points and draw with the radius. When drawing above, you must first fix the board in a straight line.

Only on behalf of personal views, don't spray if you don't like it, thank you.