M. Baskinger, Pencils before pixels: a primer in hand-generated sketching, pp.28-36, 2008.

B. Buxton, Sketching User Experiences: Getting the Design Right and the Right Design, 2007.

S. Greenberg, S. Carpendale, N. Marquardt, and B. Buxton, Sketching User Experiences: The Workbook, 2011.