The Model 413A DC Null Voltmeter is a zero-center dc voltmeter with end scale ranges from 1 mv to 1000 volts in a 1-3-10 sequence. Input impedance varies from 10 megohms to 200 megohms depending on the setting of the RANGE (VOLTS) switch. The input terminals are isolated from the cabinet and ground permitting operation from references up to 500 volts dc or 130 volts ac from ground potential. INDICATORS. In addition to the conventional meter, which has both a normal (± 10% of full scale) and expanded (± full scale) range of zero adjustment, the Model 413A has amplifier output connectors which provide an output voltage proportional to meter deflection. This feature makes it possible to use the Model 413A as a dc amplifier for use with thermocouples, etc., or to use it in conjunction with a recorder to obtain permanent records without the need for constant monitoring. USES. The Model 413A may be used for any application that calls for a dc null voltmeter. High input impedance of the instrument makes it especially valuable for resistance bridge measurements. The high voltage gain and the exceedingly low drift and noise make the Model 413A an ideal instrument for many control applications, particularly where the system must be left unattended for long periods of time.