Measurements presuppose theories

(cited in Gillies’ “Philosophical theories of probability”): 

“Against this view [operationalism] it can be shown that measurements presuppose theories. There is no measurement without a theory and no operation which can be satisfactorily described in non-theoretical terms. The attempts to do so are always circular; for example, the description of the measurement of length needs a (rudimentary) theory of heat and temperature-measurement; but these in turn involve measurements of length.” (Popper, Conjectures and Refutations, 1963)