Slide Rule- Illumination Calculator Lighting Slide Rule +Directions
Unusual slide rule from Benjamin Products and Thomas Industries of Louisville, Kentucky, is called an Illumination Calculator. "Time saving accurate answers to your Fluorescent and Mercury-Vapor Lighting problems." Cardboard slip case gives instructions for use: room ratio, number of lamps required, ballast sound comparisons, reflected glare and contrast loss, and for use as a conventional slide rule. 9" x 3-3/4". In very good condition. From an estate sale.
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