The Big Horn 19640 is a Rotape Beam-Compass. It draw circles from 2-13/16 inch to 79 inch radius. A pin is inserted thru center hole in tape body and placed at center of radius to be drawn. The tape is adjusted to required radius and drawing. To draw parallel lines, the straight edge is slided on back of body along edge of material with one hand while guiding tape end & pencil with other.
Rotape Beam CompassDraw circles from 2-13/16 inch to 79 inch radius
Rotape beam-compass
Measuring angles and securing jig in fixed place