First question. Did you buy the bias meter, or build one? The makers of one of the bias meters have some base numbers. I ran an old fixed bias Twen at idle, and then full on with the 1000 Hz sine wave at around 500mv which is kind of hot, but pedals can put 3X that much voltage in. When I did all my calculations I got something like 18 watts and with signal 27. I have found that the plate current as measured with the meter in series is very close to what actually comes all the wat to K. I can try putting a bias pro/king/whatever on one of my tube testers, and compare its reading to that of the tester. The actual readings from the Simpson watt meter, the bias pro, and the plate voltage were really pretty much right on the money with the 1000Hz signal. How accurate the Simpson wattmeter was is a mystery, as I have never calibrated it, but the 260 it runs into is right on.