Allow us, please, to summarize briefly:
(0) The measurement uncertainty is error-bounds of the
(1) If a measurement does not involve mathematical expressions
then someone can choose the statistical way he likes to
mathematically estimate|compute a subjective uncertainty .
(2) If a measurement involves known mathematical expressions
then either there is or there is not -up to now- a known, unique,
mathematical way, that is a way solely based on these
mathematical expressions alone, to estimate|compute an
(3) A vna measurement involves known mathematical expressions
and after more than ten 10 years there are now five 5 known
mathematical ways to estimate|compute a unique objective
uncertainty, each one for each of the five 5 "error" models considered
(by intermediately estimate|compute the errors of these "errors"),
as well as new one(s), the sixth 6th (or more), shall be added
as soon as the "error" model(s) of the NanoVNA will be revealed.
(4) These "errors" of "error" models are just historical names of
parameters mathematically expressed in terms to what is widely
known today collectively as "S-parameters" and thus these are
not error bounds - they are not uncertainties of the measurement.