A method of detecting signatures in message segments comprises employing a state machine for the detection of character strings in the message segments. Each of the first and the second measurement unit is configured to perform a measurement for acquiring positioning data of the respective measurement unit. A wire spring defined by an upper free-end and a lower fixed-end is cantilevered by its fixed-end to the right side plate of the magazine follower for movement with the follower in a manner that enables the free-end of such wire spring to project through the opening when the follower reaches its apogee. A first folding mirror deflects the radiation from the object plane toward the concave mirror and a second folding mirror deflects the radiation from the concave mirror toward the image plane.