Karen:

I have just purchased an instrument called a 'Histocollimator' for
realigning blocks for recuts.  It was developed and is sold by Hans
Koczinski of Capital Instruments (410-544-5485, 410-544-4625 fax).  Hans has
demo-ed this instrument at at least 2 NSH Conventions.

It requires mounting holes on the top of your microtome (I have a Microm
330).  It is also somewhat expensive - $2300.  The working principle is a
mirror that sticks to the face of your block reflects a beam of light to a
sight with crosshairs.  You align the block using the microtome's alignment
knobs.  

We have 4 different makes of mirotomes in our lab, 3 of which have their own
particular user.  These 3 folks resent any suggestion that all of the
microtomes should be aligned alike.  The multiple-user machine is the
Microm. Those of us that use it have to do recuts on blocks cut on other
machines, hence the need for an alignment tool.

Hope this helps.
Regards -
Carol
*****************
Carol B. McCollough, HT(ASCP)
Diagnostics & Histology Laboratory Manager
Maryland Department of Natural Resources
Fisheries Service
Cooperative Oxford Laboratory
904 S. Morris Street
Oxford, MD 21654