Verification and calibration
Voltage or current dividers

In this case, the problem is limited to comparing very similar resistances (differing by 10 ^–4 or less in relative value). We use a bridgehead (proportioning arm) with very fine adjustment in the vicinity of the unit ratio. Figure 19 shows how this bridgehead is assembled, using two closely-spaced resistors P and Q and a potentiometer (R, aR ) shunted to a shunt S.

Swapping the two resistors to be compared, A and X, leads to two equilibria: $\begin{array}{}\end{array}$