However, none of the described techniques also measure roll errors or more importantly allow all the various measurements to be made simultaneously so the calibration procedure is very time consuming and prone to error. The reflector assembly 28 is engaged with locators on the measuring assembly 26 and is secured with the mounting screw. 5, the displacement measuring means 44 further includes a prism 85 which directs the beam 91 from the beam splitter 86 to the retroreflector 46 and a prism 87 which directs the reflected beam 93 from the retroreflector 46 to the beam splitter 88. Although, as will be set forth in more detail below, the positioning device 34 may be manually actuatable or automatically repositioned, it is contemplated that vertical adjustment mechanism 50 will be manually adjustable. 6 is a flow diagram of a method according to the invention. 5 are optional lenses 89 between polarizing filter 92 and photosensor 82 and between polarizing filter 94 and photosensor 84. Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the Doctrine of Equivalents. Incoming beam 73 is circularly polarized. /Nums [0 6 0 R] kJl��9��.�1U64���f8 � Positioning device 34 is constructed in order to reposition the balls to known locations within volumetric space 12 within approximately 50 thousandths (0.050) of an inch. The apparatus in claim 7 wherein said bar support includes a collar made from a heat-insulating material in order to provide a grasping point to allow replacement of the ballbar. While the diameters of tile balls are certified to a known diameter, the distance between the balls is not known with accuracy. 4 of an alternative embodiment of the invention; and. stream The invention is useful for certifying both manually operated, user manipulable, as well as programmable coordinate measuring machines. Alternatively, because the calibrated surface is stably positioned at each such location, a user of a manual CMM system may readily probe the calibrated surface using a manual CMM sensing probe. However, any type of distance measuring interferometer can be used. 2, rotated counterclockwise 45° from horizontal, as illustrated in phantom in FIG. The number of changes between light and dark fringes are counted as a measure of distance. By repeating the process by moving the certification device 31 through all 12 index positions multiple times, the repeatability of the CMM 10 may be determined by comparing the corresponding measurements made during each pass through the process. Squareness evaluations of the CMM are accommodated in all combinations of two planes with standard positioning orientation as well as all three measurement planes at once. /Im18 18 0 R 2, or rotated clockwise 45° from horizontal. These prisms permit a more compact design. Three cone-pointed screws 134 mate with locators 134a (FIG. /F14 25 0 R The first asterisk is replaced by x, y or z to denote the measurement line. This provides a que to the user to manually index (74, 78) positioning device 34. A coordinate measuring machine certification apparatus according to one aspect of the invention includes a certification device having at least one calibrated surface and a positioning device for positioning the surface in multiple known locations within the measurement volume of the coordinate machine being certified. The center of each sphere may be calculated using known computational techniques common to all coordinate measuring machines.