5. Set up the reference light sensor.
a. Place the second optics bench at right angles to the first optics bench at the spot where the beam splitter is mounted.
b. Mount the second High Sensitivity Light Sensor and Aperture Bracket to the second bench. Set the Aperture Bracket to slit #5.
c. Connect a patch cord between electrical ground and a piece of bare metal on the aperture bracket.
d. Re-adjust the beam splitter and/or the position of the second bench so the laser beam illuminates slit #5 on the second light sensor.