For decades, machine tool customers tested their machine geometry according to VDA 3441 or ISO 230-2. This established a practice of the manufacturers to calibrate the machines precisely along the lines where the acceptance testing is performed, which does not give the customer sufficient information on spatial and part accuracy.
Therefore ISO 230-6 is recommending tests along arbitrarily chosen diagonals in the volume. The machine that will give good results for ISO 230-6 is mechanically superb or volumetrically compensated, or both. It will manufacture accurate parts! While the diagonal testing is well established in U.S. aerospace and defense industry, it is not common practice in Europe and Asia. Our recommendation: Test it, you will be surprised! And perhaps become our customer.