A Heathkit IM 5248 will measure IM, SMPTE method. 60 and 7000 Hz. (Internal)
Society of Motion Picture and Television Engineers.
They cared because if the optical track recording / playback wasn't
working right the sound was as bad as a 16 mm projector that has been
dropped a time too many. (I managed to drop one down a flight of stairs.)
Some amplifiers we serviced had adjustable screen voltage on the
output tubes that needed adjustment for min IM whenever replaced.
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