  Quantum physics holds the promise of enabling certain tasks with better
performance than possible when only classical resources are employed. The
quantum phenomena present in many experiments signify nonclassical behavior,
but do not always imply superior performance. Quantifying the enhancement
achieved from quantum behavior requires careful analysis of the resources
involved. We analyze the specific case of parameter estimation using an optical
interferometer, where increased precision can be achieved using quantum probe
states. Common performance measures are examined and it is shown that some
overestimate the improvement. For the simplest experimental case we compare the
different measures and show this overestimate explicitly. We give the preferred
analysis of real-world experiments and calculate benchmark values for
experimental parameters necessary to realize a precision enhancement.
