A locking device structured to maintain an activating plunger of a dispenser assembly in an inoperative position, subsequent to dispensing, so as to facilitate a single-use operation thereof and thereby preclude the potential confusion between a used and an unused single-use dispensing device. The measured value indicates the mechanical stress caused by the alternating layer sequence of a EUV reflection layer. At least, the concave surfaces facing outward jointly define a continuous curved surface.