Why the standard resistance coil are made of manganin or nicrom?

Standard resistance coils are made of manganin or nichrome due to their stable and predictable resistive properties. Manganin has a low temperature coefficient of resistance, which minimizes changes in resistance with temperature fluctuations, making it ideal for precise measurements. Nichrome, on the other hand, offers good durability and resistance to oxidation, ensuring long-term stability and reliability in various conditions. Both materials help maintain accuracy in electrical measurements and are less affected by environmental factors.