Dear John,  You have it correct in your posting (7/15/02): it's a
crummy tracking device, and does no more than what you state:  as the
roll is pulled onto the take-up spool, it is "kept aligned" by the two
leaves that collapse towards the center, thus (more or less) aligning
the roll as it passes over the tracker bar.

Good luck.  It does work with rolls that aren't too damaged, and, of
course it works with brand new rolls.  If there is a worse tracking
device in these instruments, I am not aware of it.

All the best,

Tim Baxter
Atlanta, GA