In one aspect the present disclosure refers to a supplementary device (10) for a manually operable injection device (1), the supplementary device comprising: —；a body (11) attachable to an elongated housing (2) of the injection device (1), —；at least one connector (12, 14) connected to the body (11) and connectable to the housing (2), wherein the body (11) is attachable to the housing (2) via the at least one connector (12, 14), —；a sensor arrangement (20) coupled to at least one of the body (11) and the at least one connector (12, 14) and configured to measure a longitudinal force component (F) acting between the at least one connector (12, 14) and the body (11) in a direction parallel to the elongation of the housing (2).
