An input knob for use with a touch screen device includes stationary and moveable members. The stationary member adheres to a touch screen of the device. The moveable member moves relative to the stationary member, and is secured to the surface via the stationary member. The moveable member produces touch events on the touch surface as bits of data in response to movement of the moveable member. The moveable member may include a rotary encoder. The stationary member may include conductive pads in contact with the surface and in selective contact with a conductive mass of the moveable member. The moveable member may be ring-shaped, removeable and repositionable with respect to the surface, and/or constructed of or coated by dielectric materials. The knob may lack a direct hardwired electrical connection to or through the surface. A display system includes the touch screen device and knob.