From Feynman histories to observables

We analyze a quantum observable $f$ given by the time average of a dynamical variable F along a Feynman path. We show that $f$ can be described by a (generalized) wave function satisfying the Schrödinger-like equation and measured by a meter similar to that of von Neumann. A connection with operators is established. Examples include the particle’s momentum, energy and the fractional traversal time.