The "z" Button
The "z" button changes the zero points of the pointing map. At the
start of each night, find an Almanac Bright Star, center it on the
slit, and push the "z" button. Only use the "z" button when you are
absolutely sure of the accuracy of the coordinates. Normally, the
pointing is excellent, and you should only need to "z" the telescope a
the beginning of the night.