Measuring instruments, especially ones that observe continually over time,
have a reality to them that is independent of the states that stimulate their
senses. This is the Principle of Instrument Autonomy. Although the mathematical
concept of an instrument implicitly embodies this principle, the conventional
analysis of continual observation has become overwhelmingly focused on state
evolution rather than on descriptions of instruments themselves. Because of
this, it can be hard to appreciate that an instrument which observes for a
finite amount of time has an evolution of its own, a stochastic evolution that
precedes the Born rule and Schrodinger equation of the measured system. In this
article, the two most established of the continually observing instruments, the
Srinivas-Davies photodetector and the Goetsch-Graham-Wiseman heterodyne
detector, are reveiwed with an emphasis on the autonomous evolution they
define, made explicit by application of the recently introduced Kraus-operator
distribution function. It is then pointed out how the heterodyne instrument
evolution is a complete alternative to the original idea of energy
quantization, where the usual ideas of \emph{temperature} and \emph{energy} of
a \emph{state} are replaced by the \emph{time} and \emph{positivity} of the
\emph{instrument}.
