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This paper presents an approach to designing gestures on tabletop computers by analyzing real users' gestures.
J.O. Wobbrock, M.R. Morris, and A.D. Wilson, “User-defined gestures for surface computing,” Proceedings of the 27th international conference on Human factors in computing systems, Boston, MA, USA: ACM, 2009, pp. 1083-1092. (PDF)
via dub publications