The rate at which the Mel-Temp heats the sample, and the temperature which is ultimately achieved, is set by the power level control knob; higher power levels heat the sample faster and achieve higher temperatures than lower temperatures, as shown in the figure above.  The trick to using a Mel-Temp is to match the power setting to the melting point of the material so that the heating is slow enough to give a precise and accurate melting point in a reasonable amount of time.  For example, you would not want to use a power level of "10" to determine the melting point of a substance whose melting point is 100 °C; the temperature would be rising so fast that it would be almost impossible to measure the melting point.  Ideally, you would want to choose a power level that levels off just above the substance's melting point, so the melting takes place over a longer time.  It is not always practical to take this approach, so we often choose a power level that will achieve the desired temperature in about 10 to 15 min, which is usually sufficient.  A rough rule of thumb is to set the power level such that the temperature changes 1°C per minute near the substance's melting point.

It is also possible to change the power level during the course of melting point determination.  For example, choose a higher power setting initially and then decrease it to pass slowly through the melting point.  When the melting point of the substance is unknown, it takes some degree of trial and error to determine the melting point accurately.