Augmented Reality overlays computer generated images over the real world. This requires precise knowledge of the viewing projection of the head-mounted display (HMD) and its position. Most of the previously published methods are complicated or use special equipment for the calibration process. We present a collection of calibration methods usable for fast and easy calibration of camera parameters, object/camera to tracker transformations, and image rectification, which do not need additional instrumentation or complicated procedures. They are applicable for both see-through and video-based HMDs.