A beam compass has the ability to draw circles with a radius far greater than those drawn using a regular compass. A precision made instrument, the length of the beam could be increased by joining sections of rod together. This particular model allows an independent pen, like a Rotring isograph or Staedtler Lumocolor, to be used. The size of circle is set by moving the needle point along the beam. It was used to draw a series of mileage circles on road maps for delivery companies and the like.