V3-57 (Mikrovol'tmetr) 1985
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Microvoltmeter "V3-57" from 1985 produced the Tallinn plant "Punane RET". Microvoltmeter "B3-57" is designed to measure the rms AC voltage of arbitrary shape and to convert the AC voltage into proportional DC voltage.
Documentation:
Information from collection of Valery Khartchenko