1. A method of obtaining user input, the method comprising: initiating a display of an optical tracking grid on an electronic graphical display, wherein the electronic graphical display comprises a touch sensitive screen input; detecting the optical tracking grid within a plurality of images of at least a portion of the optical tracking grid that are captured by a tracking pen device; disabling, based on the detecting the optical tracking grid, the touch sensitive screen input; determine changes among the plurality of images; determining, based on the changes, a movement of a portion of the tracking pen device; and producing, in response to determining the movement, a data set characterizing movement.