A head-mounted display device (HMD) (100) configured to be worn by a user (121) is provided. The HMD comprises an at least partially see-through display (101), a front-facing camera (102) operative to capture a first image of a real-world scene, and processing means (104) which is operative to select a calibration object from one or more real-world objects, or parts thereof, (130-135) which are visible in the first image, and derive a calibration transformation for calculating a display position based on a real-world position, such that a virtual object which is displayed on the display at the display position is aligned with a corresponding real-world object located at the real-world position, as seen by the user.