 Reichenbach’s discussion of quantum mechanics contains a (then) standard presentation of the formalism of the theory, including the Born rule and, without stating it, the Projection Postulate (see the entry on  quantum mechanics).  It is marked, however, by Reichenbach’s empiricism about meaning, by his frequency interpretation of probability, by a three-valued “quantum logic” and by a curious neglect of the major problems and of some the most important previous foundational literature. For later philosophical readers, the missing piece in Reichenbach’s discussion of the theory is the measurement problem (see the section on the measurement problem in the entry on  philosophical issues in quantum theory):  he gives no account of how the dynamical equation of the theory can account for uncorrelated measurement and object systems becoming correlated in a measurement interaction. 