With the Calvet calorimetric principle, the sample is completely surrounded by the detector (thermopile), made of crowns of thermocouples. Such a design guarantees the measurement of the total heat exchange between the sample and the surroundings through the calorimetric detector. The Calvet principle is typical for microcalorimetry (^oC) but it is also used in DSC, and in some cases in RC. Instruments based on this principle are the most sensitive. However, they are usually limited to low heating rates and moderate temperatures. In a Calvet calorimeter, the sample container is surrounded by a secondary wall. The difference of temperatures between the internal and external surfaces of the secondary wall are measured with extreme accuracy using a crown of thermocouples ("thermopile"). The geometry, thickness and thermal conductivity of the secondary wall are known, so the heat flow is evaluated using the balance at the secondary wall