Apple Macintosh 6500 - Manual (Page 191)

2 Press down on the paper clip while you turn the ring counterclockwise.
Turn the ring a very short distance. When the recessed area on the ring is
lined up with the recessed area surrounding the ring, the mouse is unlocked.
The mouse ring is unlocked when the recessed area on the
ring lines up with the recessed area surrounding the ring.
Recessed area on ring
Recessed area surrounding ring
191 Health, Safety, and Maintenance Tips