The one above was also made at TMPL, it is a Psophometer which was a true RMS auto-ranging AC dB level meter with weighted filters. The weighted filter has to resemble the audio response curve of the ear. With a built in signal generator in dB settings it becomes a Transmission Measuring Set. This was in the eighties, it is similar to this Transmission Measuring Set from Aplab, this was the only relevant link i got. I also remember that aplab also had submitted a sample of a bigger unit then. Then some nice European units also were being evaluated by the buyer.
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