D. Spikol, and J. Eliasson. The 6th IEEE International Conference on Wireless, Mobile, and Ubiquitous Technologies in Education, page 137--141. IEEE, (2010)
T. Sohn, K. Li, W. Griswold, and J. Hollan. Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems, page 433-442. New York, NY, USA, ACM, (2008)