The ESI Model 300 Potentiometrie Voltmeter Bridge is a battery-operated multiple-use dc measurement instrument. It combines in the same case a five- range potentiometric voltmeter, a three-range precision voltage source, an eight-range ammeter, a ten-range Kelvin double bridge for two-, three-, or four-terminal resistance measurements, a four-terminal resistance comparison bridge, a ratiometer, and a high-sensitivity electronic null detector.