A calibration method of an optical see-through head-mounted display of an augmented reality system including a user interface, comprising: (a) projecting a view of a virtual object corresponding to a reference object using a calibration matrix set defined on the basis of geometric information of a head model and an HMD model so that the projected virtual object and the reference object are able to be perceived through the HMD, the reference object being of known dimensions, a location and an orientation of the reference object with respect to a 3D coordinate system being known and tracked with a camera, and the calibration matrix set defining 3D-to-2D point correspondences between 3D coordinates of the virtual object represented in the 3D coordinate system and a 2D position of the virtual object in the view projected by the display, (b) changing at least one parameter within said calibration matrix set by an amount of one or more predefined incremental changes, which may be positive or negative, in response to an instruction received through the user interface, wherein the at least one parameter is changed by directly manipulating the at least one parameter, (c) projecting a view of the virtual object using the calibration matrix set including the at least one parameter changed by the amount, and (d) performing steps (b) and (c) for a parameter within the calibration matrix set other than the at least one parameter, until the virtual object projected in step (c) is substantially aligned with the reference object as perceived through the HMD, thereby adjusting the calibration matrix, wherein the calibration matrix set includes an extrinsic parameter matrix and an intrinsic parameter matrix, both matrices being defined from geometric measures of the HMD and head models; the extrinsic parameter matrix and intrinsic parameter matrix are based on a pin-hole camera model, the pin-hole camera model including a left virtual pin-hole camera and a right virtual pin-hole camera, both of the virtual pin-hole cameras having a same defined focal length; the OST HMD is a stereo AR system providing a binocular image of the projected virtual object; the binocular image is comprised of a left image and a right image, each image corresponding to the projected view of the virtual object, the left image and the right image each being provided by using the respective extrinsic parameter matrix and intrinsic parameter matrix; and the defined focal length is used for both the left image and the right image. (a) projecting a view of a virtual object corresponding to a reference object using a calibration matrix set defined on the basis of geometric information of a head model and an HMD model so that the projected virtual object and the reference object are able to be perceived through the HMD, the reference object being of known dimensions, a location and an orientation of the reference object with respect to a 3D coordinate system being known and tracked with a camera, and the calibration matrix set defining 3D-to-2D point correspondences between 3D coordinates of the virtual object represented in the 3D coordinate system and a 2D position of the virtual object in the view projected by the display, (b) changing at least one parameter within said calibration matrix set by an amount of one or more predefined incremental changes, which may be positive or negative, in response to an instruction received through the user interface, wherein the at least one parameter is changed by directly manipulating the at least one parameter, (c) projecting a view of the virtual object using the calibration matrix set including the at least one parameter changed by the amount, and (d) performing steps (b) and (c) for a parameter within the calibration matrix set other than the at least one parameter, until the virtual object projected in step (c) is substantially aligned with the reference object as perceived through the HMD, thereby adjusting the calibration matrix,