The test is carried out using the principles of calorimetry. By knowing the temperature of the steam and the amount of energy it possesses, it is possible to establish how much moisture is present. We measure this e amount of energy in the steam by condensing a sample in a known mass of water. By measuring the temperature increase in the water and knowing how much steam has been condensed to produce this temperature increase, we can calculate the amount of energy present and therefore the amount of moisture. The calculation used also takes into account the heat loss of the test equipment and accurate temperature and mass measurements are essential if accurate and repeatable results are to be obtained.