  We model quantum measurement of a two-level system $\mu$. Previous obstacles
for understanding the measurement process are removed by basing the analysis of
the interaction between $\mu$ and the measurement device on quantum field
theory. We show how microscopic details of the measurement device can influence
the transition to a final state. A statistical analysis of the ensemble of
initial states reveals that those initial states that are efficient in leading
to a transition to a final state, result in either of the expected eigenstates
for $\mu$, with probabilities that agree with the Born rule.
