where R is the resistance between the electrodes, I is the current, I0 is the maximum supercurrent, Ic is the critical current of the Josephson junctions, Φ is the total magnetic flux through the ring, and Φ0 is the magnetic flux quantum.
Although it is possible to read the DC voltage between the two terminals of the SQUID directly, because noise tends to be a problem in DC measurements, an alternating current technique is used.