Ian, G3SEK wrote:
"1. For a Bird-43 type of meter, you have to read the forward "and" the
reflected indicated "power" levels, and plug "both" of these numbers
into the little formula to calculate SWR...which involves the ratio of
those two numbers."

Yes. Bird gives:
"VSWR = 1+sqrt Pref/Pfwd / 1-sq rt Pref/Pfwd

To eliminate calculations, the Model 43 instruction book includes charts
which give VSWR when Pref and Pfwd intersect on a chart.

A VSWR slide-rule has been produced by Bird which does the same as the
charts, and more.

Bird has published a useful series of technical papers, "Watts New From
Bird" Revisited. One paper, "The Directional Wattmeter", says:
"What is the effect of load impedance on the accuracy of the THRULINE?
The design formulas show that the only imopedance influeincing the
output voltage is Zo, the characteristic impedannce of the line at the
point of measurement. Since each THRULINE wattmeter is supplied with a
section of 50-ohm line, this Zo is accurately known. The load impedance
only affects the forward and reflected power levels which the THRULINE
measures.

Where should the weattmeter be inserted? Again referring to the
formulas, we see that the elements extract a voltage proportional to
either Ef or Er. While the total E varies along an improperly terminated
50-ohm line, the component voltages do not. This is simply another way
of saying that the energy contained in the forward wave remains the same
from the source to the load where some or all of it is reflected (unless
the load is 50 ohms) and the reflected energy remains the same from the
load back to the source. Our directional power meter can, therefore, be
placed anywhere between the source and the load.

Reg`s statement:
"But it DOES affect the indicated SWR and so the indicated SWR is
incorrect." does not apply to the Bird Model 43 wattmeter.

Best regards, Richard Harrison, KB5WZI