What is one of the three functions of the hairsprings in a d' Arsonval meter movement?

In a d'Arsonval meter movement, the hairsprings are designed to return the coil to its starting position once the current is removed. This is essential for the functionality of the meter as it ensures that the needle can reset and accurately indicate a new measurement when the circuit's current changes. The hairsprings provide the necessary restoring force that counteracts the magnetic field's influence when current flows through the coil.

The ability to reset to a neutral position is crucial for obtaining precise readings, allowing the user to interpret measurements reliably and maintain the meter's overall accuracy over time.