Calculators and Adding Machines

 


Felt & Tarrant Model J Comptometer
 

Comptometer-style mechanical calculators were once among the most common and popular forms of adding machine available. Though Felt & Tarrant originally invented and marketed the actual Comptometer brand calculating device, the word 'comptometer' has since become the vernacular. Comptometers are characterized by their massive array of keys. Unlike a modern calculator which only has a single set of numeric keys and forces the user to enter numbers one digit at a time, comptometers have a column of numeric keys for each digit. This allows a skilled operator to add numbers on the machine at a very fast pace, far faster than on a conventional calculator, by striking every column of keys at once. Comptometers are designed primarily for repetitive addition. Though capable of other mathematical operations, execution is not so straightforward. In fact, most of the entities that manufactured Comptometer-style calculators ran academies which companies could send their employees to, in order to learn how to operate these machines.

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Felt & Tarrant  Model J Comptometer
Lightning Portable Adding Machine
 

The Lightning Portable Adding Machine is a device commonly referred to as an 'addometer', a popular type of calculator in the 1950s and 1960s due to their low cost and ease of use. Unlike complex comptometers and expensive 10-key calculators, addometer-style machines could be used by practically anyone, with little to no training. The controls of the machine consist of seven perforated wheels which resemble small rotary phone dials. Four of the dials are copper-colored; these dials are the cents and thousands indicators when working with currency. The perforations in the dials are marked with numbers.

To perform addition, the user inserts a metal stylus into the appropriate hole and rotates the dials until the stylus catches the hook on the right side of the dial aperture. A small window above each dial displays the sum of the numbers entered into the unit, and a slide on the left side of the machine resets the display to zero. The unit is mounted in an angled bakelite stand for easy use, but is designed to be removed from the stand and placed directly on the document being added when performing long calculations.

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Lightning Portable Adding Machine
Todd Protectograph Co. 'Star' Adding Machine
 

The Todd Protectograph 'Star' adding machine is quite small when compared to a comptometer from the same era, such as the Felt & Tarrant Model J. The front of the machine is bristling with ribbed sliders by which numbers are entered into the device. Each rib is labeled with a number mounted to an adjacent plate. To enter a number into the device, the user places their finger onto the appropriate rib and then pulls the slider down until their finger had pushed down the small button at the base of each slider. This is quite analogous to the operation of the digits dial on a rotary telephone.

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Todd Protectograph Co. 'Star' Adding Machine
Victor 6834 Adding Machine
 

The Victor 6834 uses a comptometer-style input system, with a row of sequential input keys for each digit. Although this machine is capable of displaying up to nine digits, only eight of then have input keys, as is normal for comptometers. The unit has no display; each number entered into the machine is printed on a standard roll of adding machine paper that is loaded into the back of the device.

There is a mechanical accumulator suspended from the underside of the machine, and the lever to the right of the display is used to print and erase the contents of the accumulator. Subtraction is also possible by using the lever on the left side. Unlike many other comptometers from this era, the device has no motor. All mechanical power comes from pulling the lever on the side of the machine.

Victor 6834 Adding Machine

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