deletions | additions       diff --git a/At_installation_time_the_beam__.tex b/At_installation_time_the_beam__.tex  index 43730fc..d014a2c 100644  --- a/At_installation_time_the_beam__.tex  +++ b/At_installation_time_the_beam__.tex 
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At installation time, the beam emitted by the UTM injection system needs to be aligned with the UTM inner axis. The accuracy of this alignment is that needed to keep the beam aligned with the pupil image independent of the inner axis rotation angle: this amounts to a precision of about 0.5\,mm in shear and 0.2\,milliradians of tilt. The laxness of this constraint means that this alignment needs to be done only once, as thermal drifts in alignment of this magnitude are not expected during the course of operation (of course, it would not harm to check this from time to time). A number of techniques can be used for the this  initial alignment, but manual alignment using a theodolite inserted in the UT output beam looking at both the telescope pupil and the injected light is one option. The initial coarse alignment of a beam train (requirement 1) takes place using the BCA primary fiducial as before (there exist additional options to use the UTM light injector in addition to or instead of the primary fiducial for this task, but for brevity discussion of these options will be left to a later date).