deletions | additions       diff --git a/At_installation_time_the_beam__.tex b/At_installation_time_the_beam__.tex  index f3c414c..5b946c4 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 once:  thermal drifts in alignment alignment, whether due to the motion  of this magnitude the Nasmyth table itself or of components on the table,  are not expected to exceed this magnitude  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 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).