Origin of modern calculating machines

by J. A. V. Turck

The Ludlum Machine

In 1888, about two months prior to the issue of the Burroughs recording machine patent just referred to, a patent was issued to A. C. Ludlum for an adding and writing-machine. ([See illustration on opposite page].)

Adding mechanism attached to typewriter

It will be noted by [reference to the drawings] that the scheme is that of a typewriter with an adding mechanism attached.

The details of the typewriter may be omitted, as most of us are familiar with typewriters. A feature that differed from the regular typewriter, however, was that the machine printed figures only and the carriage operated in the opposite direction, thus printing from right to left instead of left to right.

Description of Ludlum machine

A series of numeral wheels and their devices for the transfer of the tens, designed to register the totals, are shown mounted in a shiftable frame connected with the bar marked F, with the typewriter carriage, and is claimed to move therewith.

Each numeral wheel is provided with a gear marked G, which, as the carriage moves after writing or printing each figure of the item, is supposed to slide into mesh one at a time with an adding gear marked H, the engagement taking place from right to left. Or beginning with the right or units numeral wheel a higher order numeral wheel gear is supposed to shift through movement of the carriage into engagement with the adding gear H, each time a key is depressed.

The adding gear H, is supposed to receive varying degrees of rotation from the keys according to their numerical marking and to rotate the numeral wheel with which it happens to be engaged, a corresponding number of its ten marked points of registration.

Between the adding gear H, and the keys which act to drive it, is a ratchet and gear device consisting of the ratchet pawl pivoted to the adding gear H, the ratchet I⁶, and its pinion gear, the segment gear I² fast to the rock shaft I, the nine arms I¹ fast to the rock shaft and the pins I², which are arranged in the key levers to contact with and depress the arms I¹ of the rock shaft varying distances, according to the value of the key depressed. That is, supposing that the full throw of the key-lever was required to actuate the rock shaft with its gear and ratchet connection to give nine-tenths of a revolution to the numeral wheel in adding the digit nine, the pin I² in the (9) key-lever would in that case be in contact with its arm I¹, of the rock shaft, but the pins I², of each of the other key levers would be arranged to allow lost motion before the pin should engage its arm I¹ of the rock shaft, in accordance with the difference of their adding value.