A method for determining one or more errors of a rotational position establishment system is provided. More particularly, a rotary apparatus having first and second parts that rotate relative to one another about a rotation axis of the rotary apparatus is used to determine one or more rotation errors. A rotation position determination system is used to determine rotation position errors from the rotation positions of the rotary apparatus or a change in the rotation position of the rotary apparatus, and from rotation positions of a reference rotary apparatus or a change in the rotation position of the reference rotary apparatus.