Constantan refers to a copper-nickel alloy commonly used for its stable electrical resistance across a wide range of temperatures. Alternatively it is known in various contexts as Eureka, Advance, or Ferry. It usually consists of 55% copper and 45% nickel. Its main feature is the low thermal variation of its resistivity, which is constant over a wide range of temperatures. Other alloys with similarly low temperature coefficients are known, such as manganin.