Apple Macintosh 6500 - Manual (Page 190)

2 Press down on the paper clip while you turn the ring clockwise.
Turn the ring a very short distance, until it stops. When the recessed area on
the ring is not lined up with the recessed area surrounding the ring, the mouse
is locked.
To unlock the mouse, follow these steps:
1 Insert a straightened paper clip into the hole on the plastic ring.
Insert a straightened paper clip into this hole.
(The hole may be located here on your mouse.)
The mouse ring is locked when the recessed area on the ring
does not line up with the recessed area surrounding the ring.
Recessed area on ring
Recessed area surrounding ring
190 Appendix A