Signedetched and white filled on front of instrument, top right: PRECISION / CONDENSER / 100 & 1100 (greek letter mu) (greek letter mu) f / TYPE 722-D SERIAL NO. 845 / GENERAL RADIO CO. / CAMBRIDGE MASS. U.S.A.
Inscribedstamped on carrying crate: CRUFT INSTRUCTION
FunctionPossible function: a stable and precise variable air capacitor intended for use as a standard of capacitance.
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