You can use this apparatus to verify Ohm’s law, which states that voltage (V) is directly proportional to current (I), with resistance (R) as the constant: V = IR.

It includes a wire-wound rheostat, a moving coil voltmeter, and a moving coil ammeter
All components are mounted inside a case
It has four terminals, two for connecting a battery and two for the resistance coil
By varying the current and measuring the voltage, the linear relationship between V and I can be observed, confirming Ohm’s law.