When reading through books and stuffs: oftentimes you'll be presented with a formula. That formula is probably correct. However: how do you use it in a derivation correctly without wasting time deriving it yourself just to see All The Little Nuances that enter in significantly to how the equation/model is used? Example: I fumble around with negative signs in the tangent(something1) = something2-transcendental equation resulting for the eigenenergies of a quantum-finite-potential-well problem, and it's infuriating to waste time trying to use someone else's results when their sign-convention is misleading to me. Suggestions?