A calibration method for determining parameters of a portable electronic device which includes an image acquisition module to be used to determine parameters of a user and a display, where the method includes providing a known pattern, using an image of the known pattern from the image acquisition module of the portable electronic device from a first position, providing at least one indication to the user to move the portable electronic device relative to the known pattern to at least a second position different from the first position, taking an image of the known pattern in the second position using the image acquisition module, and processing the image of the known pattern taken from the second position to determine at least the parameters of the portable electronic device comprising the image acquisition module used to take the image.