A method of correcting inconsistent locations of back patches caused by magnetic interference, the method comprising: affixing back patches to the back of a patient; receiving, at a first time, from each of the back patches, a first position-dependent signal generated using a magnetic field sensor of the back patch that is configured to measure magnetic fields produced by external field generators and a first magnetic interference level signal; computing first location coordinates in a three-dimensional coordinate system comprising an X-axis, a Y-axis, and a Z-axis for each of the back patches using the first position-dependent signals and computing a first magnetic interference index for the back patches using the first magnetic interference level signals; identifying first spatial relationships between the back patches using the first location coordinates of the back patches as a first rigid body; receiving, at a second time subsequent to the first time, from each of the back patches, a second position-dependent signal generated using the magnetic field sensor of the back patch and a second magnetic interference level signal; computing second location coordinates in the coordinate system for each of the back patches using the second position-dependent signals and computing a second magnetic interference index for the back patches using the second magnetic interference level signals; identifying second spatial relationships between the back patches using the second location coordinates of the back patches as a second rigid body; detecting a discrepancy between the first and the second magnetic interference indices and a discrepancy between the first and the second spatial relationships of a plurality of the back patches relative to the remaining of the back patches, wherein the detected discrepancy indicates that the second location coordinates of the plurality of the back patches are inconsistent with the second location coordinates of the remaining of the back patches; calculating, based on the first location coordinates, location corrections for the plurality of the back patches; and applying the calculated location correction to the second location coordinates of the plurality of the back patches, thereby determining corrected second location coordinates for the plurality of back patches. affixing back patches to the back of a patient; receiving, at a first time, from each of the back patches, a first position-dependent signal generated using a magnetic field sensor of the back patch that is configured to measure magnetic fields produced by external field generators and a first magnetic interference level signal; computing first location coordinates in a three-dimensional coordinate system comprising an X-axis, a Y-axis, and a Z-axis for each of the back patches using the first position-dependent signals and computing a first magnetic interference index for the back patches using the first magnetic interference level signals; identifying first spatial relationships between the back patches using the first location coordinates of the back patches as a first rigid body; receiving, at a second time subsequent to the first time, from each of the back patches, a second position-dependent signal generated using the magnetic field sensor of the back patch and a second magnetic interference level signal; computing second location coordinates in the coordinate system for each of the back patches using the second position-dependent signals and computing a second magnetic interference index for the back patches using the second magnetic interference level signals; identifying second spatial relationships between the back patches using the second location coordinates of the back patches as a second rigid body; detecting a discrepancy between the first and the second magnetic interference indices and a discrepancy between the first and the second spatial relationships of a plurality of the back patches relative to the remaining of the back patches, wherein the detected discrepancy indicates that the second location coordinates of the plurality of the back patches are inconsistent with the second location coordinates of the remaining of the back patches; calculating, based on the first location coordinates, location corrections for the plurality of the back patches; and applying the calculated location correction to the second location coordinates of the plurality of the back patches, thereby determining corrected second location coordinates for the plurality of back patches.