  This paper develops a number of quantum mechanical characterisations of
Stern-Gerlach. It discusses areas of vagueness in their formulation.
Philosophers criticise quantum mechanics for unacceptable vagueness in
connection with the measurement problem. The quantum formulation problems
identified by this paper go beyond the locus of philosophical criticism. It
concludes with an open question, are some areas of vagueness in quantum
mechanics more acceptable philosophically than others and, if so, why?
