it is prudent to measure the melting or freezing point of each realisation of temperature with a reference standard thermocouple which should be dedicated for this purpose. An erroneous or false plateau can arise with the use of three-term temperature controllers which may hold the furnace very precisely near, but not at the fixed-point temperature. It is important, therefore, to witness the melting/freezing curve, and the undercool that precedes the temperature rise to the freezing point arrest.