A motion system includes a first stage that is configured to rotate about
a first axis and a second stage coupled to the first stage that includes
an object carrier adapted to position an object in at least one other
axis. The motion system has a novel arrangement of laser interferometer
elements and axes of motion. The arrangement permits accurate and precise
measurement of a position of the object carrier in up to three (or more)
axes of motion even as the first stage of the motion system is tilted
through relatively large angles. The novel arrangement of the axes of
motion also enables very precise control of the position of the object
carrier even at high tilt angles.