Another thing that can effect what a watt meter reads is the swr, the
length of the feed line, and where in the feed line the meter is
placed. I've repaired radios for years and have a bird as well as an ifr
service monitor and I use the watt meter more as a relative reading than
anything else. My ifr, for example usually read a bit high, while the
bird was always a bit scotch when compared to other meters.
73s
Butch WA0VJR