A more concrete example: You discover that the formula for making a beam that will have equal stress all along it's length is t = (.923)Xe/L^2 (made-up formula)

A more concrete example: You discover that the formula for making a beam that will have equal stress all along it's length is t = (.923)Xe/L^2 (made-up formula) You can not patent that formula, but you can get a patent on beams made using that formula. With that patent in hand you can stop anyone from making, selling, or using those beams.