Harris, W. J. A., Williams, J. D. S., & Wiedhaup, C. J. J. (1977). A handbook on distance education: (a handbook to brief and help administrators, educationalists, politicians and all others engaged in distance education in countries seeking to introduce, extend or improve correspondence education for adults). Department of Adult and Higher Education, University of Manchester.

Harris, W. J. A., John D. S. Williams, agus C. J. J. Wiedhaup. A Handbook on Distance Education: (a Handbook to Brief and Help Administrators, Educationalists, Politicians and All Others Engaged in Distance Education in Countries Seeking to Introduce, Extend or Improve Correspondence Education for Adults). Manchester: Department of Adult and Higher Education, University of Manchester, 1977.

Harris, W. J. A., et al. A Handbook on Distance Education: (a Handbook to Brief and Help Administrators, Educationalists, Politicians and All Others Engaged in Distance Education in Countries Seeking to Introduce, Extend or Improve Correspondence Education for Adults). Department of Adult and Higher Education, University of Manchester, 1977.