Vixen AP Equatorial Mount Instruction Manual page 39

APPLICATION
Polaris is out of place from the designated position. This is part of the process.
Since there is no mark that points at the North Celestial Pole, you
need to match the polar axis of your AP equatorial mount with the
N.C.P using the conspicuous polar star and two stars in the same
area of the sky. This is called polar alignment.
Your goal is to set Polaris to the edge of the line on the side of 2014,
and both Delta UMI and 51 Cep are to be set to the middle of the
curved lines of the position scale at the protruded edge on the side of
15 respectively. (In case of the year 2014)
★
The movement of Delta UMi from
2014 to 2040 by precession
The locations of Polaris, Delta UMi and 51
Cep on the position scales change year by
year due to precession of the Earth. You need
to compensate the locations of the 3 stars on
the position scales yearly.
Center of the polar alignment scope's field of view
(Center of the rotational axis of the equatorial mount)
Celestial north
Adjust the red light illumination to be dimmer if the reticle is
too bright to see the 4th magnitude Delta UMi.
If the 5th magnitude 51 Cep is hard to see in the polar
alignment scope's field of view, at least be sure to set Delta
UMI to the position scale on the reticle.
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Turn the polar alignment scope body so that Delta UMi comes near
to the location of the year 2014 on the scale. And then, Polaris will
get out of position from the gap between the lines.
Celestial north
★
The movement of Polaris from
2014 to 2040 by precession
★
The movement of 51 Cep from
2014 to 2040 by precession