Long before handheld calculators and smartphone apps were these slide-rule style calculators. This one, made by Line Materials, allows one to determine pole spacing, voltage drop and circuit load for a series incandescent street lighting installation.
This is too cool! I learned about determining voltage drops along a series circuit in electrical class by using Ohms Law, you can either do it on paper or on a calculator. Or simply look up the data on different series incandescent lamps, the rated voltage is the voltage drop.
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