Jockey
Jockey is a metal strip with insulated handle that used to slide over the long wire which is used as varible resistor.
- Resistance of a wire is directly proportional to it's length.
- So by sliding jockey through the wire, the wire between one terminal and the jockey is under consideration and that fraction of the length correspond to a fraction of total resistance.
- Long wire as a variable resistance gives precise and small values of resistance.