Our tweezers-style #LcrMeter uses “automatic balancing bridge method” to measure R, L and C. The diagram is as below:
R is a standard resistor which is always equal to the current flowing through the DUT (Device Under Test). The L side of DUT (lower voltage side) is always equal to the virtual ground level (electric potential = 0). At this condition, the impedance value of the DUT (Zx) can be determined from the voltage on the DUT (Vx), feedback resistance R and input voltage V1 as follows:
Zx = R * Vx / V1
Reference: Keysight Technologies Impedance Measurement Handbook – A guide to measurement technology and techniques