An analysis is made of problems associated with prediction of and correction for temperature disturbance created by thermocouples placed beneath a surface of a heat sink (or calorimeter) exposed to heat flux during re-entry. Two of the important factors affecting temperature measurement are discussed: (a) The disturbance created by the thermocouple itself, “hot spot.” (b) The fact that the thermocouple has to be placed at some distance from the heat flux surface and thus not measuring the surface temperature. The magnitude of the surface hot spot caused by the presence of the thermocouple is determined, and optimum location of the thermocouple is found where the undisturbed surface temperature may be read with least over-all error.