A medicament delivery device for injections or inhalations comprises a supplementary device affixed to it. The supplemental device is provided with an optical system for monitoring a dosage of medicament. The optical system is able to receive reflected and refracted optical images of the dosage value as the optical signals from the medicament delivery device and thus keep a dosage window on the medicament delivery device free for direct monitoring by a user due to changing the transferring of the optical signal direction. The supplemental device is able to analyze, record and display the dosage and the other relevant data on a display and inform the user. The supplemental device is also able to transmit the medicament delivery data to an external device. A method for collecting the medicament delivery data including the medicament dosage information from a dosage setting mechanism and controlling the dosage, recording and displaying the dosage data by the supplemental device on its display is disclosed. The method allows due to changing of the optical signal transmitting direction by the optical system also simultaneously monitoring the dosage window of the medicament delivery device. This method increases a safety and minimizes the dosage setting errors.
