Rolling the cryostat over bumpy cobblestone or tactile pavement can loosen the pins that hold the knife clamp arms. The microtome will probably look something like this:
Assuming everything was working just fine at the last job, all the parts should be rolling around somewhere at the bottom. Put the knife clamp arm back where it belongs.
Now find the pin and insert it into the hole.
Use your heat sink to tap the pin all the way in.
All fixed!
The next time you need to go over bumpy pavement, ROLL THE CRYO SLOWLY.
