A touchscreen can be overlaid on a tablet computer to support asymmetric two-handed interaction in which the non-preferred hand operates the touchscreen and the preferred hand uses a stylus. The result is a portable device that allows both hands to interact directly with the display, easily constructed from commonly available hardware. The method for tracking the independent motions of both hands is described. A wide variety of existing two-handed interaction techniques can be used on this platform, as well as some new ones that exploit the reconfigurability of touchscreen interfaces. Informal tests show that, when the non-preferred hand performs simple actions, users find direct manipulation on the display with both hands to be comfortable, natural, and efficient. Author Keywords Asymmetric bimanual interaction, tablet computing, touchsensitive screens, commodity hardware. ACM Classification Keywords H5.2. [Information interfaces and presentation]: User interfaces -- Input devices an...