Abstract: A superconducting magnetic sensor having a sensing coil is provided with one or more superconducting discs for adjusting the effective area of the coil. The effective area of the coil is adjusted by varying the position of the superconducting disc relative to the associated coil. In a superconducting gradiometer having a pair of sensing coils coupled in series opposition, three superconducting discs are arranged to provide effective area adjustment along three mutually orthogonal axes. Coarse and fine adjustment are optionally provided by employing two sets of superconducting discs, one set fixed, the other adjustable.