  This paper introduces a one-port method for estimating model parameters of
VNA calibration standards. The method involves measuring the standards through
an asymmetrical passive network connected in direct mode and then in reverse
mode, and using these measurements to compute the S-parameters of the network.
The free parameters of the calibration standards are estimated by minimizing a
figure of merit based on the expected equality of the S-parameters of the
network when used in direct and reverse modes. The capabilities of the method
are demonstrated through simulations, and real measurements are used to
estimate the actual offset delay of a 50-$\mathbf{\Omega}$ calibration load
that is assigned zero delay by the manufacturer. The estimated delay is $38.8$
ps with a $1\sigma$ uncertainty of $2.1$ ps for this particular load. This
result is verified through measurements of a terminated airline. The
measurements agree better with theoretical models of the airline when the
reference plane is calibrated using the new estimate for the load delay.
