The following assumes a vertical piano.  For a grand piano the method
would be adapted as needed.

If you are using a laser to check out the spool box alignment in the
front to back direction, you might as well use it to check out the top
to bottom alignment.  Using a bubble level within the spool box could
be quite a juggling act.

You can make a "laser level" by sticking a laser pointer to an impro-
vised turntable.  If there is no wobble to the spindle, the laser will
produce a straight line.  The turntable can be mounted on a good tight
hinge to use as a vertical adjustment.  With the unit mounted on a
rigid surface parallel lines can be traced on the three elements to
check their alignment.

If this same method is used from above the spoolbox, in an upright, the
front to back alignment can also be checked.  It might be necessary to
add an extension to each end of the bottom spool so that the line would
hit it and not be blocked by the tracker bar.  This eliminates the need
for a helper and a wall opposite the piano.

If you are good at adapting surplus items you can also get a line
generator [a laser lamp] from an old UPC bar code scanner.  Make sure
the line produced is straight before you trust the results as these
things can get out of alignment.

Spencer Chase