[Radio Wrangler]

The calibration of an S meter will probably also change if you can select different filter bandwidths.

Selective voltmeters were used for years monitoring and testing FDM multiplex phone trunks where they got called Selective Level Measuring Sets. All the usual culprits made them (HP3745A HP3746A etc)They usually have USB and LSB as well as a Demod output.
Because they're dedicated to measurement, the AGC steps in chunks, so it's better put to manual if you use one as a receiver. They're popular again for listening to LF/VLF signals.

There were also measuring receivers called Wavemeters as a sort of non-scanning non-crt hand-cranked spectrum analyser.

I'm afraid there are thousands of tons of boat anchors out there which beat you to it, Al.

David