Abstract: A Cartesian robot comprises a base member disposed along an x-axis, a transverse member moveably mounted to the base member, and disposed along a y-axis transverse to the x-axis. The robot has a y-carriage for a measurement probe moveably mounted to the transverse member along the y-axis. The x, y, and z axes define a Cartesian coordinate system. The robot includes an innovative structure that achieves high precision with respect to the z-axis by providing a planarized and stable reference surface along the y-axis (vertical axis). The position of the y-carriage with respect to a z-axis is a predictable function of the measured position of the y-carriage on the reference surface, and rigid-body tilt of the reference surface. High accuracy and precision are achieved by utilizing a granite slab for providing the planarized reference surface disposed along the y-axis for the transverse member.