Need to calculate Ohm’s law? Convert women’s clothing sizes? Calculate the area of a circle? Figure out whether its better to buy or rent a home? It’s all at www.calculatoredge.com.
The site has lots of formulas for the urban homsteader even if you never have to perform a Sallen-Key Butterworth Low Pass Filter equation (except, perhaps, for recreational reasons).
Thanks to Bruce Nolte, N1BN for the tip.