Take a wooden or cardboard cylinder, with a diameter equal to a fourth part of the distance you require between the spires (or trelices) to be traced. On this cylinder fasten one end of a string, B, and wind it up, and attach to the other end a pencil, C, or a point, according to what you want to do.

Now you have only to turn to right or left according to the direction in which the string was wound up, by holding the pencil down and keeping the string tight, and a spiral of perfect regularity will be traced.

The above figure clearly shows the process. The cylinder A has a diameter equal to the distance R S divided by 4.