  We propose a classification of measurement apparatuses based on their
reliability and accessibility. Our notion of reliability parameterises the
possibility of getting unexpected wrong results when using the apparatus in a
given time window, and the one of accessibility describes the energy cost
required to make the apparatus interact with a measured system. The
classification is obtained by relating an apparatus's reliability and
accessibility to the time dependence of the overlap of its pointer states. As
an example, we study a one-to-all qubit interaction in which all the qubits act
as a measurement apparatus for the one. This model shows that using randomly
selected couplings results in accessible but unpredictable measurement
apparatuses. Conversely, apparatuses with uniform coupling exhibit higher
reliability but are energetically more costly.
