The invention relates to a method and device for the polarimetric measurement of a flat object with regularly repeating patterns forming lines of a network. According to the invention, a first zero order measurement is carried out with an angle of incidence (1) for a first azimuthal angle (1), a second zero order measurement is made, with an angle of incidence (2) for a second azimuthal angle (2),the polarisation of the incident beam is modulated and the polarisation of the reflected beam analysed for each measurement, the theoretical polarimetric data for an object model of the real object are calculated, the object model having parameters which may be adjusted by means of a formalism of the electromagnetism. The object is characterised by making an iterative comparison of measured withthe theoretical polarimetric data for different values for the adjustable parameters.