This instrument is used to measure an unknown resistance.
The components are arranged in a diamond pattern so that students may quickly understand how the circuit works. Two arms of the bridge have 1/2% precision resistors of 1, 10, and 100 Ohms, each with its own individual shorting switch. These are used to establish a resistance ratio between the two sides of the bridge. Binding posts connect the unknown resistor and a resistor substitution box to the other arms of the bridge. Other binding posts connect to an external battery and a suitable galvanometer.
When the value of the unknown resistor is truly unknown, the bridge may initially be in gross imbalance. Closing the circuit on the most sensitive range might damage the galvanometer, so having the coarser ranges for preliminary adjustment is quite necessary.
The center panel is brush-finished, anodized aluminum and the one-piece bottom is painted steel.