[G0HZU_JMR]

If it doesn't work like the above then maybe this device allows you to compare the impedance at Z2 (reference) against the DUT at Z1 where the Z2 reference can be a complex impedance. It could be a resistance in series with a capacitor or an inductor for example. The deeper the null at the detector the closer the agreement between Z2 and Z1. But this would be a fairly clunky way to do things and I'm not sure how often such a device would be useful.