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The horizontal position of the light source should be placed in such a way so that the
illuminating part is at the center of rotation, as shown below. The center of rotation
is marked with a slit in the top plate.
Important:
Failing to align the light source to the center of rotation can affect the
accuracy of the peak intensity value and the beam angle.
The flux value is not affected by the incorrect horizontal placement.
Guidance on how to establish the photometric center of a light source can be found
in the next section.
