The 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.