A device for administering a fluid product includes a measuring assembly for measuring a position between spaced apart elements of the apparatus that can be moved relative to each other. The measuring assembly includes at least one magneto-resistive sensor that is fixed to a first element, such as a casing, and is arranged opposite at least a second element, such as a sleeve, which can be moved relative to the first element. A magnetic device co-operates with the at least one sensor and is formed by a permanent magnet on the first element and a magnetized second element including a magnetic surface profile or including of a number of alternately arranged, different magnetic pole areas.
