So I've been thinking about my future book titled Algebra and Trigonometry for Lighting Designers. Filled with, you know, fun stuff like this: Deriving a lighting fixture's multiplication factor from its beam angle using trigonometry: [Excel format] Multiplying Factor(MF) =2*TAN((x/2)*PI()/180), where x is the beam angle in degrees. Note: the "*PI()/180" portion of the equation is just to force Excel to express the answer in degrees rather than radians, and therefore isn't needed if calculating by hand. I've realized I need collaborators. Other than "W=VA" and "P=IE in your E=IR," what are some other formulas/calculations you use regularly? This may end up just being a pamphlet rather than a book, and will in inevitably become a wiki entry, so any/all help is appreciated.