The 895A DC Differential Voltmeter is half-rack size, and is equipped with resilient feet and tilt-up bail for field or bench use. A single instrument may be mounted in a standard 19 inch rack with metal handle-rack adapter kit 881A-102. Two half-rack size instruments may be mounted side-by-side with metal handle -rack adapter kit 881A-1Q3. The 895A can be used as: (a) A conventional voltmeter for rapid determination of dc voltages from 0 to ±1100 volts to within ±3% of range setting, (b) A differential voltmeter for precise measurement of dc voltages of 0 to ±1100 volts to within ±(0. 0025% of input +0.0001% of range + 5 uv). (c) A ratiometer for accurately determining the ratio of two voltages, and (d) A megohmmeter for measurement of resistance from 0.1 megohm to 10,000,000 megohms with a typical accuracy of ±5%. The instrument can be used to indicate voltage excursions about a nominal value. One feature that should be emphasized is that no current is drawn from the unknown voltage source, when the voltmeter is at null, at up to 1100 volts. Thus, the determination of the unknown potential is independent of its source resistance. 1-4. Leakage resistance of the 895A to ground is 100 megohms. The instrument contains a polarity switch for convenience in measuring positive or negative voltages, or in using the instrument as a ratiometer. A grounded recorder output is included for monitoring the voltage being measured. Shock, vibration, humidity, and tem - perature testing verify a design that will provide years of hard use under severe environmental conditions. When used as a differential voltmeter, the 895A operates on the potentiometric principle. An unknown voltage is measured by comparing it to a known reference voltage with the aid of a null detector. An accurate standard for measurement is provided by an 1100 volt reference supply containing a pair of temperature-controlled zener diodes. A five-dial Kelvin-Varley voltage divider attenuates the reference voltage as necessary to obtain a null condition. The unknown voltage is then indicated by the setting of the voltage readout dials.