Wittich, W. A., & Schuller, C. F. (1979). Instructional technology: Its nature and use (6th ed.). Harper & Row.

Wittich, Walter Arno, and Charles Francis Schuller. Instructional Technology: Its Nature and Use. 6th ed. New York: Harper & Row, 1979.

Wittich, Walter Arno, and Charles Francis Schuller. Instructional Technology: Its Nature and Use. 6th ed. Harper & Row, 1979.