Hmmm. Don't know any of the individuals mentioned, but the wattmeter designs are not at all similar.
Black Cat copped out and used a "narrow-band" design that would only stay calibrated over a narrow range of frequencies. It's a "RF Voltmeter" circuit with the scale calibrated in Watts. Pretty accurate into a dummy load or other low (1.1) SWR. Soon as you change frequency by more than a MegaHertz or so, the calibration goes out the window.
One of my favorite demos 25 years ago was to take a 3-Watt 2-meter ham HT and patch it into a Black Cat wattmeter, driving the dummy load. Because the Black Cat used a capacitor tapped off the coax center-wire, it was roughly 100 times more sensitive on 146 MHz as it was on 27 MHz. Sure got some suprised looks from the CB operators when my battery-powered HT showed 300 or 400 Watts on the Black Cat meter. I would assure them that it was a "false" reading, and not to be trusted.
The Dosy meters mostly used a current probe design, with the coax center wire passed through a toroid coil. Not too different from the Drake and Heathkit wattmeters, but modified to "sorta" read peaks. The higher the power range you select, the closer it will come to reading actual "PEP" power. On the lowest range, peak readings will tend to be a bit stingier. It's a trait shared by nearly all other "passive" peak-reading RF Wattmeters.
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