An on-body sensor system, comprising: a plurality of skin interface units for coupling electrical signals into and/or out of the body of a subject, including two or more reference units (34a, 34b), each for placement against a respective known region of the skin, and at least one positionable unit for placement at a further unknown position, each of the reference units comprising at least two pairs (52a, 52b) and the positionable unit comprising at least one pair of skin coupling electrodes; and a controller operably coupled with the skin interface units and adapted to control transmission of signals through the body between the positionable unit and the reference units, derive at each reference unit one or more signal characteristics associated with signals received at each pair of electrodes respectively of the unit, and based on this derivation to derive an indication of an angle of arrival of signals at the reference unit, access a reference dataset comprising information indicative of known angles of arrival of signals at reference units corresponding to said reference units being are placed at said known regions of the skin, and the signals being received from reference units being placed at locations corresponding to one or more of said other known regions of the skin, and derive an indication of position of the at least one positionable unit based on the derived angles of arrival of signals and on the information in the reference dataset, and generate output information based on the derived indication of position. a plurality of skin interface units for coupling electrical signals into and/or out of the body of a subject, including two or more reference units (34a, 34b), each for placement against a respective known region of the skin, and at least one positionable unit for placement at a further unknown position, each of the reference units comprising at least two pairs (52a, 52b) and the positionable unit comprising at least one pair of skin coupling electrodes; and a controller operably coupled with the skin interface units and adapted to control transmission of signals through the body between the positionable unit and the reference units, derive at each reference unit one or more signal characteristics associated with signals received at each pair of electrodes respectively of the unit, and based on this derivation to derive an indication of an angle of arrival of signals at the reference unit, access a reference dataset comprising information indicative of known angles of arrival of signals at reference units corresponding to said reference units being are placed at said known regions of the skin, and the signals being received from reference units being placed at locations corresponding to one or more of said other known regions of the skin, and derive an indication of position of the at least one positionable unit based on the derived angles of arrival of signals and on the information in the reference dataset, and generate output information based on the derived indication of position. control transmission of signals through the body between the positionable unit and the reference units, derive at each reference unit one or more signal characteristics associated with signals received at each pair of electrodes respectively of the unit, and based on this derivation to derive an indication of an angle of arrival of signals at the reference unit, access a reference dataset comprising information indicative of known angles of arrival of signals at reference units corresponding to said reference units being are placed at said known regions of the skin, and the signals being received from reference units being placed at locations corresponding to one or more of said other known regions of the skin, and derive an indication of position of the at least one positionable unit based on the derived angles of arrival of signals and on the information in the reference dataset, and generate output information based on the derived indication of position.