Roger Waring expressed his preference for systems that move tracker
bars.  I, too find they do less damage to rolls.  However, since they
must move all the mass of tubing and the tracker bar itself, they
don't easily make the quick, micro-adjustments that I like to see in
a tracker system.

One of the more unusual tracker systems I've seen was in a player
from Canada.  It had five holes on each side of the tracker bar.
One pair of holes would be open at any one time and these would act
as the tracker system.  If you wanted to transpose, a different pair
of holes would open, and the tracker pneumatic would move the bar until
once again, the roll would be in balance.  The tracker pneumatic had
tremendous range and was cumbersome, but it worked!

Jeff Davis -- in sunny (for the moment) Seattle.