Why spring balance shows incorrect reading after long time?

A spring balance may show incorrect readings over time due to the fatigue of the spring, which can lose its elasticity from prolonged use or overloading. Additionally, environmental factors such as temperature fluctuations can affect the spring's properties, leading to inaccuracies. Dust, dirt, or rust on the mechanism can also interfere with its operation, causing inconsistent measurements. Regular calibration and maintenance can help mitigate these issues.