When using cameras on telescopes, there are times when the camera must be rotated to place
a guide star on the guiding chip or to provide better framing of an object. If you only intend to only gather
one night's worth of sub frames, it is not too important to keep track of the camera's relative rotation.
However, if you intend to take sub frames over a number of nights or perhaps over a number of years, the rotation
of the camera becomes very important as you typically will want to use the same framing or guide star to keep
the sub frames consistent.
On the Sky90, I used a very simple system. I placed a reference mark on the focus tube
coupler and used a piece of tape corresponding with the reference mark on the CAA with the object's name/number
for future use. Any time I wanted to image the object I simply rotated the CAA until the object's tape label
lined up with the reference mark. However, after a number of years, I ended up with a CAA totally covered
with smudged pieces of tape that I could no longer read. I needed a better system...