An apparatus comprising: at least one receiver configured to receive signals relating to a place and orientation of a device relative to a head, the device being capable of inducing an electric field in the head, a location in the head where the electric field is induced depending on a place and orientation where the device is, the strength of the electric field in the location depending on the place and orientation of the device; at least one processing core configured to determine, at least in part based on the received signals, the place and orientation of the device relative to the head, and to cause signals to be transmitted, wherein the at least one processing core is configured to compare the place and orientation of the device relative to the head to information concerning a place and orientation of the device corresponding to a maximal induced electric field strength being induced in a treatment area, wherein the transmitted signals are configured to cause a display to indicate a deviation of the place and orientation of the device from the place and orientation corresponding to the maximal induced electric field strength being induced in a treatment area, characterized in that, additionally, upon the device being placed in the place and orientation corresponding to the maximal induced electric field strength being induced in the treatment area, the apparatus is configured to indicate a deviation such that changing the place and orientation of the device to eliminate the deviation increases the induced electric field strength in the treatment area but does not change a specific location inside the head where the induced electric field strength is maximized, wherein the at least one processing core is configured to calculate strengths of induced electric field at a specific location based at least in part on a model of the head. at least one receiver configured to receive signals relating to a place and orientation of a device relative to a head, the device being capable of inducing an electric field in the head, a location in the head where the electric field is induced depending on a place and orientation where the device is, the strength of the electric field in the location depending on the place and orientation of the device; at least one processing core configured to determine, at least in part based on the received signals, the place and orientation of the device relative to the head, and to cause signals to be transmitted, wherein the at least one processing core is configured to compare the place and orientation of the device relative to the head to information concerning a place and orientation of the device corresponding to a maximal induced electric field strength being induced in a treatment area, wherein the transmitted signals are configured to cause a display to indicate a deviation of the place and orientation of the device from the place and orientation corresponding to the maximal induced electric field strength being induced in a treatment area, characterized in that, additionally, upon the device being placed in the place and orientation corresponding to the maximal induced electric field strength being induced in the treatment area, the apparatus is configured to indicate a deviation such that changing the place and orientation of the device to eliminate the deviation increases the induced electric field strength in the treatment area but does not change a specific location inside the head where the induced electric field strength is maximized, wherein the at least one processing core is configured to calculate strengths of induced electric field at a specific location based at least in part on a model of the head.