Lightning Portable Adding Machine  
Written by AnubisTTP on 2007-07-04  


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.


As its name implies, the Lightning adding machine is primarily designed to perform only addition. There is a procedure for performing subtraction on the Lightning, but it is quite cumbersome. In subtraction, the values in the windows are ignored. Instead, values are indicated by the red arrows on each dial. To subtract, the user rotates the dials until the red arrows are pointing to the value that they wish to subtract from. Numbers to be subtracted are entered into the machine normally, by placing the stylus in the appropriate hole and rotating the dials to the right. The final value is indicated by the numbers opposite the red arrows on each dial. Compared to other mechanical adding machines which use the complementary math system, the Lightning's subtraction procedure seems rather awkward, and contrary to its efficient addition function.

Lightning Portable Adding Machine
Lightning adding machine, shown with base, stylus, original box and manual.

Lightning Portable Adding Machine Stylus
Entering digits into the Lightning.

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