The accompanying illustration gives a top view of the instrument. The following description is taken from the Engineer, 20th May, 1870.

It is constructed chiefly of a brass plate A A furnished with eight slots as shown; directly under these slots are mounted eight drums, each having nine elongated cog-teeth of successively decreasing length; over each drum, and between it and the slot, is mounted a square shaft on which slides a pinion wheel, so as to catch any number of teeth on the drum. Each of these pinion wheels is moved by a button a, of which there is one in each slot, the figures at the sides of the slots showing the proper position of each button a for any work to be performed by the instrument, so that not the least trouble is encountered in arriving at the result. The cogged drums gear by bevel wheels with a long horizontal shaft which is also in gear with the vertical shaft moved by the handle b, by which the instrument is worked. B B is a moveable brass plate, which can turn and slide on a round bar hinge at the back; in this plate there are sixteen holes, c, under each of which is a moveable disk numbered from 0 to 9, and arranged so that any one figure of each disk may be brought under its corresponding hole c.