U.S. WWII Army Signal Corps Frequency Meter BC-221 T from ZENITH. This Meter is not tested ! Comes incl Operation Book ! The BC221 is both a HF generator and a heterodyne frequency meter covering 125 kHz to 20 MHz with an accuracy of about 100 Hz, designed in the USA during the 2nd World War (1941-1942) to provide fighting units with an accurate means of setting the frequency of transmitters and receivers. What you see is what you get !