A drug delivery system (100, 200), comprising: - a drug-filled cartridge or means for receiving a drug-filled cartridge, the cartridge comprising an outlet and an axially displaceable piston, - first sensor means comprising one or more sensors each adapted to measure a magnetic field corresponding to at least two axes, - second sensor means comprising one or more sensors each adapted to measure a magnetic field corresponding to at least one axis, - an expelling assembly for expelling an amount of drug from a reservoir, comprising: - setting means allowing a user to set a dose amount of drug to be expelled, - actuation means for releasing or driving the drug expelling assembly to expel the set dose amount, and - an indicator element adapted to rotate during expelling of an amount of drug, the indicator element comprising a magnet moving together therewith, the magnet being configured to generate a spatial magnetic field which relative to the sensors varies corresponding to the spatial orientation of the magnet and thus the indicator element, thereby generating a spatial magnetic field which varies relative to each sensor as the indicator element moves, - processor means configured to: (i) on the basis of measured values from the first sensor means, determine a rotational position of the indicator element, (ii) calculate an expelled dose amount based on determined rotational positions of the first indicator means, (iii) on the basis of measured values from the second sensor means, determine a high-speed condition in which the rotational speed of the indicator element exceeds a given threshold level, and (iv) indicate an error state if the high-speed condition is detected, wherein the processor means and sensor means form part of an electronically controlled capturing system for capturing data representing a property related to the amount of drug expelled from the reservoir by the expelling assembly during expelling of a set dose, the property being rotational movement of the indicator element. - a drug-filled cartridge or means for receiving a drug-filled cartridge, the cartridge comprising an outlet and an axially displaceable piston, - first sensor means comprising one or more sensors each adapted to measure a magnetic field corresponding to at least two axes, - second sensor means comprising one or more sensors each adapted to measure a magnetic field corresponding to at least one axis, - an expelling assembly for expelling an amount of drug from a reservoir, comprising: - setting means allowing a user to set a dose amount of drug to be expelled, - actuation means for releasing or driving the drug expelling assembly to expel the set dose amount, and - an indicator element adapted to rotate during expelling of an amount of drug, the indicator element comprising a magnet moving together therewith, the magnet being configured to generate a spatial magnetic field which relative to the sensors varies corresponding to the spatial orientation of the magnet and thus the indicator element, thereby generating a spatial magnetic field which varies relative to each sensor as the indicator element moves, - setting means allowing a user to set a dose amount of drug to be expelled, - actuation means for releasing or driving the drug expelling assembly to expel the set dose amount, and - an indicator element adapted to rotate during expelling of an amount of drug, the indicator element comprising a magnet moving together therewith, the magnet being configured to generate a spatial magnetic field which relative to the sensors varies corresponding to the spatial orientation of the magnet and thus the indicator element, thereby generating a spatial magnetic field which varies relative to each sensor as the indicator element moves, - processor means configured to: (i) on the basis of measured values from the first sensor means, determine a rotational position of the indicator element, (ii) calculate an expelled dose amount based on determined rotational positions of the first indicator means, (iii) on the basis of measured values from the second sensor means, determine a high-speed condition in which the rotational speed of the indicator element exceeds a given threshold level, and (iv) indicate an error state if the high-speed condition is detected, (i) on the basis of measured values from the first sensor means, determine a rotational position of the indicator element, (ii) calculate an expelled dose amount based on determined rotational positions of the first indicator means, (iii) on the basis of measured values from the second sensor means, determine a high-speed condition in which the rotational speed of the indicator element exceeds a given threshold level, and (iv) indicate an error state if the high-speed condition is detected,