The circuit is just for a relative field strength meter so your unknown meter will either be more sensitive, less sensitive or the same sensitivity as the designer intended. Personally I would just replace the resistors with a 100K variable resistor and use your meter as it is and it will be just as useful.
I have never found field strength meters to be particularly useful around the shack. For antenna experiments I measure aerial current:
This parameter is far more meaningful than VSWR or field strength.
Yes, that’s a a perfectly valid and cheaper way of doing things. Thank you. As Geoff said, I “couldn’t see the wood for the trees”. I want an FSM for making A/B relative comparisons between different antennas.
The current meter does indeed look very useful, and again simple although calibrations looks like it requires quite advanced kit. It is yet another thing I have desired but not wanted to shell out for! I’ll look into constructing one of these as well.