Väyrynen, S., J. Röning, and I. Alakärppä. “User-Centered Development of Video Telephony for Servicing Mainly Older Users: Review and Evaluation of an Approach Applied for 10 Years”. Human Technology, vol. 2, no. 1, Apr. 2006, pp. 8-37, doi:10.17011/ht/urn.2006157.