The Hewlett-Packard Model 427A is a versatile, compact, self-contained voltmeter. It is capable of making de measurements from 1 mV to 1000 volts, ac measurements from 0. 3 mV to 300 volts at frequencies from 10 Hz to 1 MHz, and resistance measurements from 0.2 ohms to 500 megohms. With the 01 option, the Model 427A may be powered either by a 115 or 230 volt line or by an internal 22-1/2 volt dry cell battery. 1-3, The use of solid state components throughout gives the Model 427A both ruggedness and reliability. Battery operation makes the instrument ideal for field use or isolation from common mode ground loops.