Test device for the horizontal dispersion of a laser beam and corresponding method

The device (10) has a telescope including a flat image sensor (5) e.g. CCD chip, arranged in an image plane (4) of a magnifying objective (3), and capturing an image of a laser beam (L) incident on the objective. A natural inclination compensator and an evaluating unit (7) determine an image position of the beam captured in the image based on image processing, and quantify a laser beam horizontal trueness by converting the determined image position into a laser beam inclination value based on a conversion rule, which relates to calibration parameters that depend on a position of the sensor. Independent claims are also included for the following: (1) a system of a laser beam horizontal trueness-testing device and a laser beam projection device (2) a method for testing a laser beam horizontal trueness of a laser beam projection device.