Lightning Portable Adding Machine [Detail]  
Written by AnubisTTP on 2008-01-29  

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 adding machine, shown with base, stylus, original box and manual.

Entering digits into the Lightning.

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