The Isothermal range of Thermocouple Standards are the result of many years development. The type R and S standards will cover the range from 0°C to 1600°C. The measuring assembly comprises a 7mm x 300mm or 600mm gas tight 99.7% recrystallized alumina sheath inside which is a 2.5mm diameter twin bore tube holding the thermocouple. The inner 2.5mm assembly is removable since some calibration laboratories will only accept fine bore tubed thermocouples and some applications require fine bore tubing. The covered noble metal thermocouple wire connects the measuring sheath to the reference sheath which is a 4.5mm x 250mm stainless steel sheath suitable for referencing in a 0°C reference system. Two thermo electrically free multi-strand copper wires (teflon coated) connect the thermocouple to the voltage measuring device. The thermocouple material is continuous from the hot or measuring junction to the cold, or referencing junction.