Here's why:

* Temperature Coefficient of Resistance: This value indicates how much a material's electrical resistance changes with temperature. A zero temperature coefficient means the resistance remains nearly constant regardless of temperature fluctuations.

* Constantan: An alloy of nickel and copper, constantan is specifically designed for its low temperature coefficient. It's used in applications where resistance needs to be stable even under varying temperatures, such as precision resistors and thermocouples.

Other materials with low temperature coefficients:

* Manganin: Another copper-nickel alloy with a very low temperature coefficient, often used in standard resistors.

* Nichrome: A nickel-chromium alloy known for its high resistance and good resistance to oxidation, making it suitable for heating elements. While not as low as constantan, its temperature coefficient is still relatively low.

It's important to note that no material has a *completely* zero temperature coefficient. There will always be some minor variation in resistance with temperature.