A position sensor having a circular transmitter coil which generates electromagnetic radiation when excited by a source of alternating electrical energy. The system may include a first medium processing apparatus, a host apparatus, and a second medium processing apparatus. The offset cancellation element is able to adjust to the initial unwanted capacitances of each sensor as well as dynamically adjust to changes in the unwanted capacitance due to the environment. According to this example, the ROI may be automatically identified, or identified based on receipt of user input identifying the ROI.