Methods, devices and systems for location of the disposition of a medical probe in a subject are disclosed. An array of electromagnetic drive coil sets, each set having two or three dimensionally oriented drive coils, a sensor coil being electromagnetically communicative with the array of electromagnetic drive coil sets, a discrete core wire providing response to electrical stimuli of the subject, and a system controller communicative with and adapted to energize one or more of the electromagnetic coils in the array of electromagnetic drive coil sets are disclosed. The energizing of the one or more of the electromagnetic coils including one or more of energizing the coils singly, or in pairs of x-y and y-z or x-z coils while measuring the response of the sensor coil, whereby the system uses the measurements of the responses of the sensor coil to calculate the location of the sensor coil relative to said drive coil sets.
