X. Zhang, Y. Qu, L. Giles, and P. Song. CHI '08: Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems, page 677--680. New York, NY, USA, ACM, (2008)
B. Evans, and S. Card. CHI '08: Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems, page 989--998. New York, NY, USA, ACM, (2008)