Thermocouple cables and extension wires allow the accurate and electronic measurement of temperature and have numerous industrial applications in specialist and extreme environments. They generally comprise two strands of conductor made of different metals, one being the positive conductor and the other the negative conductor. The two dissimilar metals in the thermocouple cable are electrically joined at the sensing point. When heated the metals produces a thermoelectric charge (Electro Motive Force, or EMF), which changes as the temperature increases or decreases. The EMF (measured in millivolts) that arises is proportional to the temperature difference between the two conductors at the sensing point. Different temperature applications require different metal conductors, different jacketing/sheathing materials and different calibration. Thermocouple cables are therefore available in a broad range of combinations of conductor, jacketing and calibration. Each pair calibrated to suit a different temperature range and environment. The most common types are manufactured to IEC Specifications J, K, T, N and IEC colour Codes. They are also available in many other local colour codes.