

Relative power? A phone and an app that shows you the received signal strength. Wifianalyzer on F-droid for example.
For me, setting it from max power to 6% (lowest value) took it from -30dBm on my couch to -50 dBm, so 20 dB difference, which is ca. 1/100. So it roughly checks out.
Keep in mind that radio waves are magic, and the higher in frequency you go, the darker the magic gets.
Absolute power is hard, especially if you are interested in average power for, like, health concerns. WiFi works in short bursts over a pretty large part of the spectrum, and you’d need calibrated equipment as well. I knew a guy who did radio wave strength mapping for like government, telcos and concerned residents, and he had a car full of tech. Simple field probes can be reasonably priced, but you need to know how to operate and interpret them.
I don’t know about their monarchy, and I don’t care. Our 19th century grandparents were too mild on the aristocrats, if you ask me. Abdicate or get the French treatment.
You should get cash for reasons that are obvious to anyone with two brain cells: if there is a blackout or cyber attack or failure of the internet, you can still pay by cash. The fact that people don’t use cash now is irrelevant. Nobody sits at candlelight listening to a battery powered radio right now either.
As a fellow pervert, I welcome my swedish siblings.