Horizon Fitness HTS-580 Series Operation Manual page 34

Reference: How to Collimate
Point the telescope toward a light surface or sky. Turn the diopter ring and adjust the
diopter so that the cross hairs are clearly observed.
Aim the target at the peak of the triangle mark of the sighting collimator. Allow a
certain space between the sighting collimator and yourself for collimating.
Focus the target with the focusing knob.
If parallax is created between the cross hairs and the target when viewing vertically
or horizontally while looking into the telescope, focusing is incorrect or diopter
adjustment is poor.
This adversely affects precision in measurement please eliminate the parallax by
carefully focusing and using the diopter adjustment.
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