  The design and operation of a quantum-mechanical device as a laboratory
instrument puts models written in equations of quantum mechanics in contact
with instruments. This contact is recordable in files of a Classical Digital
Process-control Computer (CPC) used both to calculate with the equations and to
manage the instruments. By noticing that equations and instruments make contact
in a CPC, we rewrite equations of quantum mechanics to explicitly include
functions of CPC-commands to the instruments. This sets up a proof that a
scientist's choice in linking mathematical models to instruments is
unresolvable without guesswork to narrow the set of models from which one is to
be chosen.
  As for implications of the proof, scientists inherit choices from the past
and frame choices for the future, choices open to guesswork and visible in CPC
files. To picture these choices, we adapt colored Petri nets, and the
availability of these net fragments makes choice and guesswork part and parcel
of physics.
  Net fragments as a means of expressing guess-demanding choices are applied to
portray guesswork needed in testing and calibrating a quantum computer. The
sample size required to test a quantum gate in a quantum computer is shown to
grow as the inverse square of the error allowed in implementing the gate.
