This part of ISO 230 specifies diagonal displacement tests which allow estimation of the volumetric performance of a machine tool. Complete testing of the volumetric performance of a machine tool is a difficult and time-consuming process. Diagonal displacement tests reduce the time and cost associated with testing the volumetric performance. A diagonal displacement test is not in itself a diagnostic test, although conclusions of a diagnostic nature may sometimes be possible from the results. In particular, when face diagonal tests are included, a direct measurement of the axes squareness is possible. Diagonal displacement tests on body diagonals may be supplemented by tests in the face diagonals, by tests parallel to the machine axes in accordance with ISO 230-2, or by the evaluation of the contouring performance in the three coordinate planes as defined in ISO 230-4. Diagonal displacement tests may be used for acceptance purposes and as reassurance of machine performance where parameters of the test are used as comparison index.