Abstract: A substrate (17) is probed after the planarity between a chuck (16) (or the substrate (17)) and a surface of the probing system (20), such as the bottom surface of the interface (28) or test head (22), has been checked. In one method, a measuring tool (30) having a sensor (36) is placed on a chuck (16) of the probing system (20). A distance between a sensor (36) and a surface within the probing system (20) is measured using the sensor (36). The surface is relatively flat. The sensor (36) remains spaced apart from the surface during the measuring. The measuring tool (30) is removed from the chuck (16). The substrate (17) is placed over the chuck (16) after removing the measuring tool (30) and is probed using the probing system (20). Alternatively, more than one sensor (36) can be used. Further, the sensor(s) (66, 76) could be integrated into the chuck (16), interface (28), or test head (22), thereby not requiring a separate measuring tool (30). Additionally, the method can be automated.