Virtual Museum > The early ones > simple adding machines
The COMPTOMETER
This one is interesting because it was one of the first calculators with direct input for all digits and immediate calculation. As soon as you push the number it is added to the total. Here is an early ad from the Scientific American magazine of 1902
Originally designed by Dorr E. FELT in 1887, he created the first prototype out of a wooden box, using common household items.
Here is a portrait of Mr FELT
here is an extract of the original patent from 1887
If you are curious, you can download the full patent below:
Patent 371496 from 1887The idea is very simple: by pressing the corresponding key, the lever travels differently and moves the wheel on the left by a certain number of degrees. The number 1, being on the left on the image above, you can see that this is the smallest travel.
The most complicated mechanism was in the wheel itself, to be able to carry over the 10 to the next wheel.
Many different models were made between 1900 and up to 1950's with improved mechanism and added details. The main component change was the box itself, which changed from the first wooden ones, to metal.
Of course, the first wooden boxes are the most valuable for a collector, but are extremely rare now. Not unusual to see prices starting around $800 for them.
The one I have in my collection is a newer model with a metal box, but still in very good shape:
The company manufactured these devices for many years, and I recently found a tool that must have been used for training: it's called the Comptometer Educator. Basically a small scale version of the device.
Interesting enough, Dorr FELT also patented a device called the COMPTOGRAPH, which was basically a comptometer with a printer. I have never seen one of these, but we can see the design in the patent below:
Patent 405024 from 1889
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