A method of preparing at least parts of a medical device for application and a medical assembly for preparing or storing the at least one disposable unit (1) of the medical device is disclosed. The medical assembly comprises a chemical or physical monitoring device (4) for counting and/or displaying a time period of application and/or remaining before required disposal or replacement of the disposable unit (1). The monitoring device (4) is automatically activated by moving the at least one disposable unit (1) relative to a second unit (2 9 18) of the medical assembly for:- preparing or positioning the disposable unit (1) for use with the medical device- assembling the at least one disposable unit (1) and the medical device and/or- withdrawing the disposable unit (1) of a storage compartment (3) of the second unit.
