A trammel is usually used when you have to draw a big circle or arc that cannot be handled by a regular compass. Some of these trammels can be used with a beam to make up a beam compass. A beam compass is used to scribe circles and the radius length. The circles and radius length can be changed by moving the trammel either towards the center of the beam or towards the outer end of the beam. Trammel heads can also be used to bisect lines and angles. This tool has a pointed end that can usually be replaced with a pen, pencil, crayon, or soap stick in order to mark different materials.