The invention relates to a method for carrying out a soiling check of the measurement window (3) of a measuring device (10) for checking sheet material (1), to a measuring device (10) which carries out the method, and to a device (20) for processing a sheet material comprising the measuring device. According to the invention, for the soiling check of the measurement window (3), only areas (4) of the measurement window are used which correspond, in terms of width and position in the beam path of the light, to the areas (2, 2') of the checked sheet material (1) which are checked during the checking of the sheet material. As a result, fewer cleaning steps are needed for the measurement window.
