Fluke 893a Differential ac/DC voltmeter; This unit is in excellent shape and fully working . It is capable of measuring down to a millivolt from 1100v AC or DC. It is unusal in that it uses a calibrated Kelvin/Varley bridge system to determine the voltage reading with the meter indicating a null from the bridge and the input voltage. It is likely this was a a precision lab-type instrument at one time. Its accuracy is phenominal; DC input Resistance 100 Mohms .01% to 1100V: AC .05 to .1 % at 1100V