deletions | additions       diff --git a/At_installation_time_the_beam__.tex b/At_installation_time_the_beam__.tex  index 6ae4a24..f3c414c 100644  --- a/At_installation_time_the_beam__.tex  +++ b/At_installation_time_the_beam__.tex 
...
At this point, the primary fiducial can be switched on and the downstream beam aligned with the UTM injected beam, using BEASST to compare the tilt and shear of the two beams. Further alignment of the fringe tracker and piston terms (requirements 4 and 5) can then proceed as in the original system.   To maintain alignment of the optical train in the presence of thermal drifts during the night (requirement 3), BEASST can either be used in its original mode with starlight, or the UTM alignment source can be switched on while slewing between stars (or any other convenient time) and used to check for thermal drift in any of the optics in the beam relay optical train. Any relative drift in tilt of the UTM alignment source with respect to the FTT camera is compensated for by resetting the FTT fiducial point using the spot seen on the FTT camera.