Mechanical and architectural drawings have sometimes required circles with diameters of several feet instead of the several inches possible with a standard drawing compass. A beam compass was usually sold with just the points, which the user attached to the ends of a metal rod or wooden slat the length of the desired radius of the circle. One end was held in place, and the other end was pivoted around that end, maintaining contact with the paper. The patent model in the collection is a beam compass.
