  We construct a rigourous model of quantum measurement. A two-state model of a
negative temperature amplifier, such as a laser, is taken to a classical
thermodynamic limit. In the limit, it becomes a classical measurement apparatus
obeying the stochastic axioms of quantum mechanics. Thus we derive the
probabilities from a deterministic Schroedinger's equation by procedures
analogous to those of classical statistical mechanics. This requires making
precise the notion of `macroscopic.'
