The Stern-Gerlach experiment was one of the early illustrative example
s of the Bohr view of quantum mechanics. In the Bohr view, a measureme
nt is an interaction between a quantum object and an apparatus which a
cts in a classical fashion. There are still open problems with this co
ncept, many of which enter into the discussion of the original Stern-G
erlach measurement. (C) 1998 American Association of Physics Teachers.