These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century.
- Mfd = microfarad or μF
- kc = kilocycles or kHz. 1,000 cycles per second.
- μμf or mmf = pF (picofarad)
The change from kc to kHz and mc to MHz were done because someone though that Heinrich Hertz ought to be given credit for his work.
Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the electromagnetic waves predicted by James Clerk Maxwell's equations of electromagnetism. The unit of frequency, cycle per second, was named the "hertz" in his honor. ... The SI unit hertz (Hz) was established in his honor by the International Electrotechnical Commission in 1930 for frequency, ... It was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, "cycles per second" (cps).
Many commercial and amateur radios were labeled kc or mc. My 1960s Collins S-Line manuals didn't use kHz or MHz.
Informal and deprecated terminology, from Wikipedia:
The picofarad (pF) is sometimes colloquially pronounced as "puff" or "pic", as in "a ten-puff capacitor". Similarly, "mic" (pronounced "mike") is sometimes used informally to signify microfarads.
Nonstandard abbreviations were and are often used. Farad has been abbreviated "f", "fd", and "Fd". ... μ "micro" ... was also substituted with the similar-sounding "M" or "m", which can be confusing because M officially stands for 1,000,000 (or 1,000), and m preferably stands for 1/1000.
In texts prior to 1960, and on capacitor packages until more recently, "microfarad(s)" was abbreviated "mf" or "MFD" rather than the modern "µF". A 1940 Radio Shack catalog listed every capacitor's rating in "Mfd.", from 0.000005 Mfd. (5 pF) to 50 Mfd. (50 µF).
"Micromicrofarad" or "micro-microfarad" is an obsolete unit found in some older texts and labels, contains a nonstandard metric double prefix. It is exactly equivalent to a picofarad (pF). It is abbreviated μμF, uuF, or (confusingly) "mmf", "MMF", or "MMFD".
Summary of obsolete capacitance units: (upper/lower case variations aren't shown)
- µF (microfarad) = mf, mfd
- pF (picofarad) = mmf, mmfd, pfd, µµF