Peak reading vs RMS, Dosy vs. Bird
As have been said before, a Bird without a peak reading kit will read like a Dosy 4000 series set on RMS and the Dosy can be calibrated to the Bird or to any other RMS measuring standard. A Dosy set to peak reading mode will read about 70% of true PEP (when the meter is new), a true PEP measurement requiring an oscilloscope or an active peak reading meter.
The stigma of a Dosy reading happy watts is unfounded as those making this claim are probably comparing the peak reading mode reading of a Dosy to a Bird meter without a peak reading kit installed. Another possibility is that someone may have calibrated their Dosy meter improperly to over-read. The Bird 43 has the capability to be outfitted to measure up to 10 kilowatts or somewhat over 3dB more than the Dosy 4000 series meters. The Bird is industry standard for commercial use at higher power levels and becomes impractical, cost-wise for the average radio operator. Furthermore, the Bird is inherently a wattmeter, so other measurements such as SWR, modulation must interpolated from power measurements. The Dosy 4000 series has calibrations and measurements for power, swr, and modulation (SSB and AM), and the high end models have an audio monitoring circuit for actual audio monitoring through headphones. For the average radio hobbyist up to the enthusiast level, the Dosy is absolutely useful to help optimize your station. The Bird is best suited for professional users