The invention relates to a measuring device (10) and a method for operation thereof. The measuring device (10) has two measuring units (12), (13), each having a probe unit (16), (35). Each probe unithas a probe element (18), (37). Each probe element (18), (37) has, in a probing direction (x), an outer probe side (18a) or (37a) and an inner probe side (18i) or (37i) opposite the outer probe side.In order to determine a zero position or a reference plane (B) at right angles to the probing direction (x), the two probe elements can be brought into contact via their respective outer probe sides (18a), (37a) or their respective inner probe sides (18i, (37i). As soon as one of the two probe units (16) or (35) detects the contact between the associated probe sides (18a), (37a) or (18i), (37i), areference plane (B) is defined as zero position in the probing direction (x) by means of the point of contact between the two probe elements. The zero position can thus be determined easily and precisely without calibrated standards or block gauges.