Kirchhoff's Pen: A Pen-based Circuit Analysis Tutor. - Ruwanee de Silva; David Tyler Bischel; WeeSan Lee; Eric Jeffrey Peterson; Robert C. Calfee; Thomas F. Stahovich (SBIM, 2007)

Newton's Pen: A pen-based tutoring system for statics. - WeeSan Lee; Ruwanee de Silva; Eric Jeffrey Peterson; Robert C. Calfee; Thomas F. Stahovich (Comput. Graph., 2008)