A device for drawing dotted lines when drafting by hand. The plate beneath the gear-like wheel is placed against the straight-edge with the wheel resting on the straight-edge face. Pulling the device along the straight-edge causes the toothed wheel to rotate, which rotates a smaller "pattern" wheel on the same axis. As the pattern wheel turns, projections on its circumference strike a lever that lifts and drops the pen point (Grimes 2018). This example from Charles Bruning Co. came with six pattern wheels (one missing), each of which has a different arrangement of projections to draw various types of dotted and dashed lines. Dotting pens remained in use until computers replaced hand drafting in the early 1990s.

The dotting pen was invented by E. O. Richter in 1874 and patented in 1875, then manufactured and sold by the E. O. Richter Co. (Planimetrica Collection 2024). Dietzgen, another drafting supplier, lists a Dotting Pen manufactured by Richter in their 1904 catalog. Richter's patents ran out around 1905, and by 1907 Richter instruments are no longer found in the Dietzgen catalog. Presumably, Dietzgen had started manufacturing their own version. Virtually identical versions were also sold by Kern, Charles Bruning and other drafting suppliers. A dotting pen in the 1926 Dietzgen catalog sold for $5.15 (Dietzgen 1931, 103).