A test apparatus for measuring the relative flatness of a side of an object. The test apparatus includes an electronic probe immobilized in a surface plate such that the contact member of the electronic probe is adjacent to the plane of the surface plate. The use of a surface plate directly eliminates the dial indicator and the trio of stands and their problematic features such as translating the flatness of the surface plate. The use of a high resolution probe permits the relative flatness of the surface plate to be taken into account for the first time. For example, to enhance the accuracy of the relatively high resolution of which the electronic probe is capable of measuring, the flattest portions of the testing surface of the surface plate are determined and the bore in which the electronic probe is set is drilled in one of the "most flat" portions. To protect and isolate the probe and its contact member from especially the industrial or manufacturing environment, the size of the opening for the contact member in the testing surface of the surface plate is minimized. To reduce friction between the side of the object and the contact member, a roller is utilized as the contact member. To reduce errors in measurement, the probe is set at a right angle to the plane defined by the testing surface. To provide access to the probe, the surface plate includes a hand sized opening formed in a nontesting surface of the surface plate.