[ARC Tech-109]

Both are nothing more than a milliamp meter measuring cathode current, guess if absolute accuracy is a concern one could measure this using ohms law and a resistor, I believe but don't quote me the CRT cathode current is about 1.4 ma for full emissions for the triad gun, maybe someone can verify and correct me on this.
I've owned my 466 since the late 80s and trust the accuracy all the way. The only change I made was to replace the G1 pot with a 10-turn and add corrections to the G1 readings on the meter using my Fluke 77 and converting the cable end to a Molex connector so I could use the 467 sockets and make my own for testing computer monitor CRTs way back then.
The numbers are subjective and a marginal CRT can test good with 6.3V on the heaters, drop the heater voltage and note the readings and how quickly they fall off, I've also found a "marginal" reading CRT to look good and retain the emissions with reduced heater voltage and hold the color tracking.
One thing about the 466 is the rejuvenate functions are much softer than the older brute force designs as they use a light bulb as a ballast, they're also a little more refined than the earlier ones but again accuracy subjective.