A drug delivery system including: an oblong housing including a setting structure to set a dose of a drug via an angular position; and a sensor structure to determine the dose, including a magnet and a magnetic sensor, arranged so that at least one of an angular position and a displacement of the magnetic sensor relative to the magnet may be determined as a function of the electrical resistance of the magnetic sensor. The sensor structure is arranged in relation to the setting structure so that the angular position of the setting structure is determined as a function of the angular position and/or the displacement of the magnetic sensor. A sensor structure is also described including: a flexible foil, including a magnetic sensor, in a cylindrical shape configuration comprising an axis; and a magnet arranged at a line parallel to or collinear with the axis.