A dosage measurement system is adapted to receive a motion from a dosage injection mechanism disposed within a drug injection pen. The dosage measurement system includes a substrate, a sensing capacitor disposed on the substrate, and a lifting tab. The sensing capacitor includes a dielectric layer disposed between a base plate and an adjustable plate. The lifting tab is attached to the adjustable plate and positioned to engage an undulation pattern disposed on a component attached to the dosage injection mechanism. The lifting tab is adapted to physically change a separation distance between the adjustable plate and the base plate in a reciprocal manner in response to the motion of the dosage injection mechanism and engagement with the undulation pattern. A capacitance of the sensing capacitor changes in response to the engagement of the lifting tab with the undulation pattern and the motion of the dosage injection mechanism.