 The feature of imprecision and approximation plays a prominent rôle in the structuralistic programs. In the context of the measurement problem, imprecision seems to be a defect of the theory which impedes the exact determination of the theoretical quantities. However, imprecision and non-uniqueness is crucial in the context of evolution of theories and the transition to new and “better” theories. Otherwise the new theory could in general not encompass the successful applications of the old theory. Consider for example the transition of Kepler’s theory of planetary motion to Newton’s and Einstein’s theories: Newtonian gravitation theory and general relativity replace the Kepler ellipses with more complicated curves. But these should still be consistent with the old astronomical observations, which is only possible if they don’t fit exactly into Kepler’s theory . 