The present invention relates to a glass plate (2) for use in a device (1) for stretching sample sections having a sectioning knife, the glass plate (2) being arranged at the back (3) of the sectioning knife in such a way that a defined gap (4) for reception of the sectioned sample is formed between the back (3) of the sectioning knife and the plate (2), the glass plate (2) possessing, at least on one of its longitudinal sides (21, 22), edges (211, 212; 221, 222) ground and polished to optical flatness.