The paper describes an instrument for measuring capacitances from –10 µµF to +10 µµF and resistances from 10 ohms to 10000 ohms at frequencies up to at least 1000 Mc/s. The instrument may be fed from the a.c. mains or from a vibrator unit supplied by a 6-volt battery. The voltage impressed on the unknown impedance is low enough for use on receivers. The two scales are direct reading in micro-microfarads and ohms. The accuracy attained is approximately 1%.