A method and an apparatus for controlling exposure of a surface of a substrate in a process of structuring the substrate with light of a predetermined intensity are described, wherein the light is directed to the surface by means of a deflectable mirror. The side wall of the box can also be turned in essentially the direction of the base, in which case the said parts folded on top of each other are joined to form a continuation of the wall. The lug has a free edge which, when the collar is in the unclamped state, faces towards the hook, and the tongue carries at least one retaining member which, when the collar is in the unclamped state, lies in a cavity provided under the lug and co-operates with the free edge thereof. The status signals indicate the data repetition status of that repeater unit to the integrator.