"Antonio Vernucci" wrote in news:4640a649$0$17940
:

We are talking about millivolt levels, but the good news is that today,
stable high gain DC amplifiers are a snack (see chopper stabilised Op
Amps).

Yes, but to my knowledge, the Struthers wattmeter is purely passive, no
amplifier whatsoever.


You have misunderstood me, my post was in answer to your more general
question "Does anyone know of special diodes resulting in a linear
wattmeter scale?" (which I quoted in my post).

If you weren't interested in the answer to the question, why ask it?

Owen