An apparatus and method for detecting the angle of passive rotary knob partially located on a touch screen are described. In embodiments the apparatus includes a touch screen having an array of sensors and a dial that includes a base and a knob attached to the base and rotatable relative to the base. The knob includes a plurality of conductive elements, each positioned a distance from a center point of the knob. A controller is also included, coupled to the touch screen, and configured to receive signals generated by one or more sensors of the array in response to the sensors detecting one or more of the conductive elements. The controller can determine a rotational angle of the knob based on the signals generated by the one or more of the sensors in the array while a portion of the knob does not overlap the array of sensors.