  Since S-parameter measurements without uncertainty cannot claim any
credibility, the uncertainties in full two-port Vector Network Analyser (VNA)
measurements were estimated using total complex differentials (Total
Differential Errors). To express precisely a comparison relation between
complex differential errors, their differential error regions (DERs) were used.
To demonstrate the method in the most accurate case of a direct zero-length
thru, practical results are presented for commonly used Z-parameters of a
simple, two-port, DC resistive T-network, which was built and tested against
frequency with a VNA measurement system extended by two lengthy transmission
lines.
