Apparatus (2) configured to assist a user in correctly positioning the apparatus on a drug delivery device (1), the apparatus comprising: attachment means for attaching the apparatus to the drug delivery device； an imaging arrangement for capturing at least one image of a portion of a delivery device； a processor for processing the captured at least one image to determine a position of the apparatus relative to the drug delivery device and to determine a manner in which the apparatus should be moved in order to correctly position the apparatus on the drug delivery device； and a display for displaying an indication of the manner in which the apparatus should be moved in order to correctly position the apparatus on the drug delivery device.
