Gimbal instrument having a prealigned and replaceable optics bench

A method includes providing: an optics assembly including a housing, a beam splitter, and a position detector; and an alignment fixture; placing the assembly on the fixture which makes contact with the assembly on the first region; projecting the third beam of light onto a first surface; rotating the assembly about the sixth axis on the fixture; sensing a change in a position of the third beam of light in response to rotation of the assembly about the sixth axis; adjusting the first path to align the third beam of light to the sixth axis; attaching the assembly to a dimensional measurement device; directing the third beam of light to a retroreflector target; reflecting a portion of the third beam from the target as a fourth beam of light; and sending a third portion of the fourth beam from the beam splitter to the position detector.