Photograph of drawing of wire calculator, Southern California, 1931. "Square D Calculator, Copyright 1931 by Frank A. Short, Los Angeles, Patents Pending, Motor Data Based on National Electric Code; Feet One Way; Wire Size; Percent Drop; Amperes; 440 Volt, 18-28-D.C., System, 220 Volt, Index, 120 Volt, 110 Volt; Wire Calculator, Based on Resistance Drop Only. To Find Wire Size or Distance: Set amperes to proper system index, turning disk in slot at top of calculator, then turn knob until allowable percent drop appears in round window - distances and corresponding wire sizes now appear opposite each other. To Find Percet Drop: Set amperes to proper system index - turn knob until selected wire size appears opposite the distance to center of load-read percent drop through round window. To Find Amperes: Set selected wire size opposite to distance then turn lower disk until allowable percent drop appears in round window-read amperes at proper system index. Amperes, R.C. Wire, Cond.3 W; [T]o Find Amps Non-Inductive Load, Multiply KW. by Constant, System, Voltage, Constant, Current in Common Wire of 3 Wire 2 Phase System = L41 x Current in Phase Wires; Diamond Electrical Manufacturing Company, Ltd., Affilliated with Square D Company, Los Angeles" -- signage on drawing. "Photo by 'Dick' Whittington" -- on frame. "1320 E[ast] 16th St[reet]" -- address on drawing.