 In Chapter VI, von Neumann (1955) discussed the conceptual distinction between observed and observing system. In this context, he applied (1) and (2) to the general situation of a measured object system (I), a measuring instrument (II), and (the brain of) a human observer (III). His conclusion was that it makes no difference for the result of measurements on (I) whether the boundary between observed and observing system is posited between I and (II &amp; III) or between (I &amp; II) and III. As a consequence, it is inessential whether a detector or the human brain is ultimately referred to as the  “observer”.[7]