There is provided an imaging unit comprising at least one image sensor, a measuring instrument including at least one marker, a position computing unit, a determining unit, and an output controller, wherein the imaging unit is configured to acquire an image comprising a user and the marker, and provide the acquired image to the position computing unit, wherein the position computing unit is configured to compute a position of the marker with respect to the user based on the image provided by the imaging unit, and further provide the computed position to the determining unit, wherein the determining unit is configured to determine whether the computed position of the marker matches a retrieved measurement position, and further output the result of the determination to the output controller, and wherein the output controller is configured to provide an indication when the marker position matches the measurement position.
