The M-SURE 535 series digital depth gauge not only measuring depth but can used for checking alignment, in this instance for setting up a magnetic encoder rail parallel to the slideway. Using the wide base of the gauge against the slideway or fixed point, zero the gauge at one end and then measure at the opposite end. Adjust the rail until you get a zero reading at each end. The same method could be used to set a work piece parallel on a milling machine table.