In industrial high frequency dielectric heating, heating cycles involving rates of temperature increase up to three hundred or four hundred degrees (F) per minute are common. It is important to know the values of the dielectric properties of the substance heated over the whole range of the heating cycle. Conventional methods of measurement, such as ASTM shunted susceptance, are not available as they all involve the steady state, and such low values of stress that there will be no appreciable loss or rise of temperature during the measurement.