In a rotated die error, one of the dies spins around its vertical axis.  In the case of a normal, in-collar rotated die error, it is impossible to determine which die has rotated.  Complex and compound rotated die errors -- where the die rotation is combined with at least one other error -- do allow us to determine which die rotated.  In the vast majority of cases, the hammer die is the culprit.

     Die rotation errors can be stable or dynamic.  This 1994 cent shows a stable rotated die error.  Relative to the obverse die, the reverse die shows a 165 degree counterclockwise rotation.