The physical observations that lead to quantitative physical theory are “pointer-readings.” The observational data consist of statements to the effect that, when one given set of pointers are incident on certain scale divisions, then another set of pointers are incident on such and such scale divisions. “Pointers” and “scale divisions” are here used in a generalised sense. The question arises as to how it is possible on the basis of a collection of incidence relations of this sort to build up a quantitative theory i.e. one involving the concept of measurement. It must be noted that until this is done any numbers associated with scale divisions serve merely as labels.