Sinclair Radionics, 1979
PFM200, or pocket frequency meter, was one of
the last instruments produced by Sinclair Radionics
before its split into two companies (Sinclair Instruments,
later Thandar, and Sinclair Research). It had a frequency
range of 20 Hz - 200 Mhz with a resolution of 0.1 Hz.
Very much like its companion product, the PDM35
multimeter, the PFM200 was housed in cases originally
manufactured for the Oxford
range of calculators earlier in the 1970s.