A
magnetic detector locates magnetically tagged items, such as
surgical sponges or instruments, introduced to and remaining in the
body cavity of a surgical patient. The
magnetic detector is a wand or probe that is manually handleable, and spatially manipulable and moveable, by an operator, such as a medical professional. The
detector is moved about at a spatial location of an ambient
magnetic field at the patient and
operating table. A characteristic of the ambient
magnetic field at the spatial location is saved by the
detector. The
detector is subsequently moved about at the same spatial location. If any magnetically tagged item is present in the vicinity of the detector during this subsequent movement at the spatial location, an anomalous
magnetic effect is detected by comparison of the prior detection reading absent the tagged item to the detection reading in presence of the tagged item in the patient. The anomalous
magnetic effect, and thus the tagged item, is locatable spatially in the patient, by three-dimensional sensor(s), arrays of sensors, and pluralities of arrays of sensors of the detector. The different detection readings with and without presence of the anomalous
magnetic effect caused by presence of the tagged item in the patient are calculable as scalar, vector array, and / or gradient array determinations, according to the particular number and configuration of sensors in the detector.