Signedunsigned
Inscribedengraved on right side of base plate: THE CENTIGRAPH / PAT / JUNE 9. 91 /
1453.
FunctionThe centigraph is a mechanical adding machine. Users input the desired numbers using the key pad. For numbers greater than five, two keys can be depressed simultaneously. Every input number is added to the counter. The counter is the visible numeral display on the front most disc. The counter can count up to 99. However, the arrow on the front most disc can point to any number from 1 to 5 and these are the hundreds position. Therefore, the adding machine can count up to 599 at which point the adding machine must be reset by putting the arrow back to its outermost position and resetting the counter.
The following description of the key pad, spring mechanism, and counting of the instrument is taken from the original curatorial cards that accompany the instrument:
"Rods with keys 1 through 4 pass under [a horizontal] shaft [at the base of the discs] curving up-wards from under discs and connecting on left with the two levers holding discs in place. When key is depressed, rod presses shaft upwards, which releases one lever, allowing small-toothed disc to turn. Immediately afterwards, spring coil on right end of shaft expands to left, pushing a little vertical catch before it which catches a tooth and stops the disc. Key rod pushing up from below keeps catch from moving any farther to left. If 3-key is depressed, catch slides 3 spaces to the left until it hits 3 rod and is stopped: that distance equals the distance of three teeth on disc. When 5-key is depressed, it hits directly the lever holding large-toothed disc stationary (it does not - like the other key-rods-pass underneath discs and shaft). Disc is released until it is stopped by catch at other end of lever, 5 spaces around the edge (corresponding to only one of the large tooth-gaps). When 1-key is depressed successively, numbers under window increase by ones; when 2 lever is depressed they advance by twos, and so on through fives."