A scarce Professor Willis's brass odontagraph by HOLTZAPFFEL of London.

Also sometimes spelled 'odontograph', an instrument for setting out the teeth on gear wheels.

Marked 'PROFESSOR WILLIS'S ODONTAGRAPH MADE BY HOLTZAPFFEL & Co LONDON' on the shorter arm with 'SCALE OF CENTRES INSIDE THE PITCH CIRCLE OUTSIDE CENTRES' with the graduated scale on the other.

 9 inch and 13¹/₂ inch long arms with both being 1³/₈" wide.

A few minor surface scratches, please see images.

A fine example of a rare item.