  Measurement is the only part of a general quantum system that has yet to be
characterized experimentally in a complete manner. Detector tomography provides
a procedure for doing just this; an arbitrary measurement device can be fully
characterized, and thus calibrated, in a systematic way without access to its
components or its design. The result is a reconstructed POVM containing the
measurement operators associated with each measurement outcome. We consider two
detectors, a single-photon detector and a photon-number counter, and propose an
easily realized experimental apparatus to perform detector tomography on them.
We also present a method of visualizing the resulting measurement operators.
