A device for analyzing a transparent surface of a substrate including a reference pattern facing a surface of the substrate to be measured. The reference pattern is formed on a support of short and long extents. A camera is provided for taking at least one image of the reference pattern distorted by the measured substrate. A reference pattern illumination system and a processor for processing the image and digital analysis are connected to the camera. The support is of oblong shape and the reference pattern is a one-directional pattern that extends along the shortest extent of the support. The pattern is transversely periodic to the short extent, and the camera is a linear camera.