On Tue, 23 Dec 2008 04:20:26 -0800 (PST), Richard Fry
wrote:

A table
on Page 3 there shows a measurement uncertainty at the NIST test
facilities of ±1/4 to ±1 dB, depending on the DUT and the frequency
range.

Actually, ±1 dB would be the most likely error for instrumentation
error (±¼ dB could never be achieved); matching error would compound
that; the antenna would add another ±1 dB; path would scramble that
further if not performed in an anechoic chamber or on a calibrated
range.

Mac's test system (from fig. 15 he reports in other correspondence)
would accumulate up to the several dB he reported earlier. It would
exhibit a very good relative accuracy, but absolute accuracy would be
several dB error as he has already offered in prior correspondence.
Path problems would have to be hammered out on their own.

73's
Richard Clark, KB7QHC