National Telecommunications & Information Administration 1980. L.R.Bloom; A.G.Hanson; R.F.Linfield; D.R.Wortendyke (October 1980). VIDEOTEX Systems and Services(PDF) (Report). U.S. Department of Commerce, National Telecommunications & Information Administration, Institute for Telecommunication Sciences, Boulder, Colorado. NTIA Report 80-50. Archived from the original(PDF) on 6 June 2011. Retrieved 1 February 2010.
National Telecommunications & Information Administration 1980. L.R.Bloom; A.G.Hanson; R.F.Linfield; D.R.Wortendyke (October 1980). VIDEOTEX Systems and Services(PDF) (Report). U.S. Department of Commerce, National Telecommunications & Information Administration, Institute for Telecommunication Sciences, Boulder, Colorado. NTIA Report 80-50. Archived from the original(PDF) on 6 June 2011. Retrieved 1 February 2010.