Abstract: A gauge for a coordinate measuring machine has a plurality of balls whose centers are located on at least one line inclined with respect to a reference axis in a virtual reference plane. The gauge is set on a measuring table of the coordinate measuring machine. Orthogonal coordinates in which one of the coordinate axes is identical to the reference axis are set in the virtual reference plane. The coordinates of the center of each ball are measured by the coordinate measuring machine. Thereafter, the gauge is turned and inverted by 180 degrees about the reference axis and is set again on the measuring table. Orthogonal coordinates in which one of the coordinate axes is identical to the reference axis are set in the virtual reference plane. The coordinates of the center of each ball are measured in the same way as above. Thus, measurement errors of the straightness of the machine axes of the coordinate measuring machine and the orthogonality between the machine axes can be easily and precisely evaluated.