The disclosure relates to an injection device for setting and injecting pre-set or user-selectable doses of a medicament, the injection device comprising an elongated housing defining a longitudinal direction and configured to accommodate a cartridge containing the medicament, and a detector arrangement operable to detect a relative movement between a first element and a second element. The first element is subject to a first movement relative to the second element along a first longitudinal direction for setting of a dose, the first element is subject to a second movement relative to the second element along a second longitudinal direction for dispensing of the dose, one of the first movement and the second movement is a helical movement, and the other one of the first movement and the second movement is a sliding movement in the longitudinal direction. The second element comprises at least one reference element fixed to the second element.