Dustin Freeman Hrvoje Benko Meredith Ringel Morris Daniel Wigdor ShadowGuides: visualizations for in-situ learning of multi-touch and whole-hand gestures. 165-172 2009 ITS https://doi.org/10.1145/1731903.1731935 conf/tabletop/2009 db/conf/tabletop/its2009.html#FreemanBMW09