Shoebox Comptometers - The Mechanism

The Comptometer is a remarkable achievement of the Victorian era when the economies of Europe and America were exploiting the industrial opportunities provided by the arrival of interchangeable parts.

(Bottom View)

Underneath it all...

Once the case is removed, the bottom view presents a forest of metal parts, wires, etc.; a beautiful example of classical "tight metal" engineering. This view shows the frame structure where every column is virtually identical to its neighbors. The sole exception is on the left side where no column of keys exist but where the spacing is required for the hi-order result wheel.

Comptometers were designed for parts to be interchangeable across columns in the interest of simplifying production, reducing inventories and easing repairs. While this may seem rather obvious today, the economic benefits were just beginning to have an impact back in the 1880s.

(Front View)

What's up front...

The row of result wheels comprise the "answer register". The individual wheels are color-grouped similar to, altho not the same as, the key-columns above. The rightmost column differed in that it's wheel mechanism had no need to accept carries while the leftmost wheel existed solely to receive carries from its righthand neighbor.

Note that the pictured machine has an extra righthand column probably for "sub-penny" values. Such special purpose configurations were routinely available on special order but not very common.

How many columns?...

In the earliest days, the vast majority of Compts were delivered with either 8- or 10-columns keyboards, with most of the 10-column machines used in goverment offices, banks and utilities.

(Front View) Twelve (and more) columns were available but never became popular simply because most operations involved large quantities of small value calculations, primarily additions and multiplications. The 12-column machine pictured is a late "J" and has a handle bolted to the keyplate (on top, near the patent plate) to assist in hefting its considerable weight. In a small 1893 promotional booklet ("Stop to Think"), there was even a 16-column listed altho it is doubtful if any were produced.

Surprisingly, a 20-column shoebox Compt was produced sometime after 1920! I've come across this picture in the Winter-1938 issue of Comptometer News. One cant help wondering what statistics the Burmah Railways kept that required such a monster calc. Note the Compt logo on the desk front indicating that perhaps the machine weight required the substantial support afforded by a special metal desk. This M-model 20-column also was produced in the post-shoebox era as well as a half-keyboard version.

Interestingly, Felt & Tarrant's fiercest competitor, Burroughs, always marketed their line of machines with 1 more column than the Comptometers in their long running battle for market share.

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