#$%^&*AU2016213820A120170323.pdf#####ABSTRACT A method, using multiple patches fixed to a surface of a body, the patches including respective electrodes in contact with the surface, and at least one of the patches configured to output a signal in response to a magnetic field applied to the body. Initially, the signal is processed to compute first magnetic and first electrical locations of the at least one of the patches. Subsequently, the signal is processed to compute second magnetic and second electrical locations of the at least one of the patches. A first relation is computed between the first magnetic and electrical locations, and a second relation is computed between the second magnetic and electrical locations. When there is a difference between the first and the second relations, a magnetic location correction is computed responsively to the difference, and the correction is applied in tracking a position of a magnetic tracking sensor inside the body. 30 2845397vl5/6 APPARENT LOCATIONS CORRECTION METHOD 150 AFFIX BACK PATCHES TO A PATIENT RECEIVE, FROM THE BACK PATCHES, FIRST 152 POSITION-DEPENDENT SIGNALS AND FIRST MAGNETIC INTERFERENCE LEVEL SIGNALS COMPUTE FIRST LOCATION COORDINATES AND A FIRST 154 MAGNETIC INTERERENCE INDEX FOR THE BACK PATCHES 4156 IDENTIFY FIRST SPATIAL RELATIONSHIPS BETWEEN THE BACK PATCHES RECEIVE, FROM THE BACK PATCHES, SECOND 158 POSITION-DEPENDENT SIGNALS AND SECOND MAGNETIC INTERFERENCE LEVEL SIGNALS 160 COMPUTE SECOND LOCATION COORDINATES AND A SECOND MAGNETIC INTERFERENCE INDEX FOR THE BACK PATCHES IDENTIFY SECOND SPATIAL RELATIONSHIPS 162 BETWEEN THE BACK PATCHES 164 DETECT A DISCREPENCY BETWEEN THE FIRST AND THE SECOND MAGNETIC INTERFERENCE INDICES AND A DISCREPENCY BETWEEN THE FIRST AND THE SECOND SPATIAL RELATIONSHIPS OF A PLURALITY OF THE BACK PATCHES CALCULATE, BASED ON THE FIRST LOCATIONS FOR THE 166 MORE THAN ONE OF THE BACK PAT
