Most products come with instructions on how to check the calibration of the laser level. Generally, you position the laser level some 5 to 10 meters from a wall. The laser is activated and the laser lines are evaluated if they are within the acceptable levels of tolerance according to the specifications of the manufacturer. The laser is then turned a full 180-degrees either on its mount or on a tripod and the lines are evaluated again. These need to be checked against the specifications of the manufacturer. If you’re not sure, it is often best to bring the laser level to a service center.