The equations of physics describe a process through time, while those of economics do not describe a process at all, but merely the final equilibrium point, a hypothetical situation that is outside of time and will never be reached in reality. Furthermore, they cannot say anything about the path by which the economy moves in the direction of the final equilibrium position. As there are no constant relations between any of the elements which the science of action studies, there is no measurement possible, and all numerical data available have merely a historical character; they belong to economic history and not to economics as such. The positivist slogan, "science is measurement," in no way refers to the sciences of human action; the claims of "econometrics" are vain.

Mises