Shown is a simple, reliable manner of monitoring a process of expelling a variable dose of medicament from an injection device by analyzing mechanical feedback of the injection device with reduced requirements on signal data memory space and processing power. Specific measurand and mechanical user feedback sensor configurations enable sensor signal data from which individual dosage units of expelled drug are identifiable at moderate sampling rates. Preferred configurations include a force sensor adapted to measure an axial force component as applied to the device by a user pressing a proximal injection button, and a direction sensor adapted to measure an azimuth angle of an orientation of the device. The specific measurands, or process quantities observed, relate to feedback means of the device including a resilient element that produces a number of successive mechanical feedback events proportionate to a dose or quantity of drug expelled from a medicament reservoir.
