Abstract: An apparatus for the checking of coordinate measuring machines and machine tools is described. The apparatus is a low cost and low weight ball cube with balls that can be probed with three probe styli each (with probing points distributed over more than a hemisphere in each case), the probe styli directed normal to five different cube sides. These properties are obtained by giving the balls an offset from the cube. The increased susceptibility to structural instabilities by the low weight design (e.g. plate structure) in connection with the offset balls is compensated by the use of corner connectors for the cube-edges to mount the balls on. The measurements on the ball cube yield--after evaluation--the linear approximations of the parametric errors of Cartesian axes machines: three errors of position, three errors of squareness, three roll errors, three yaw errors, and three pitch errors.