Describe the three  common features in an indicating instrument ?
- Deflecting devices: Whereby the mechanic force is produced by the current voltage or power. This force causes the moving system to deflect from its zero or null position.
- Controlling device: This device ensures that the deflection of the pointer for a given value of measured quantity always has the same value.
- Damping devices: This device always produce a force which quickly brings the moving system to rest in its final position after being deflected.