Describes a system of colour coding for twin compensating cables for thermocouples which will show the type of thermocouple with which the compensating cable is to be used and also polarity of individual conductor. Applies to following five thermocouple combinations which constitute most common thermocouples: copper v. constantan, nickel chromium (chromel and T1 alloy types) v. constantan, iron v. constantan, nickel chromium v. nickel aluminium (chromel v. alumel, and T1 alloy v. T2 alloy types), and platinum rhodium v. platinum. Combinations not covered by above list are so infrequently used that their inclusion would not be justified.