An exemplary method includes 1) detecting an initialization action performed by a first extremity of a user and a second extremity of the user, the initialization action comprising a touching of a first arbitrary location on the touch screen by the first extremity and a touching of a second arbitrary location on the touch screen by the second extremity, 2) designating, in response to the initialization action, the first arbitrary location as a first reference position and the second arbitrary location as a second reference position, 3) detecting one or more tapping actions performed on the touch screen, 4) determining a relative position on the touch screen of each of the one or more tapping actions with respect to the first and second reference positions, and 5) identifying one or more data entry commands associated with the one or more tapping actions. Corresponding methods and systems are also disclosed.