In this paper we review the basis of the technique for thermoelastic stress analysis and, in particular, we examine the relationship between the theory and the technique in common practice. The theory of thermoelastic stress analysis is based on the thermomechanical behavior of bodies, which takes strain and temperature as state variables that are path-independent, whereas the conventional instrumentation used in thermoelastic stress analysis involves an integration of photon flux derived from a body's surface temperature, and hence is time- and path-dependent. This inconsistency might be negligible for some, or perhaps most, applications. However, in those cases where the waveform of the loading is irregular, experiments have shown that the difference can be significant. The nature of most apparatus for thermoelastic stress analysis implies that this results is important when conducting experiments in which the forcing signal is unknown or not sinusoidal.