It was printed by Crowell-Collier Educational Corporation from about 1967–1992 (1967 was cited from the 1969 edition).
The encyclopedia volumes are also arranged like a dictionary, with each volume being of a uniform size separated by words, instead of by the letter of the alphabet.
There were also "Student Guides" which give a brief overview of certain topics.
Also, "Highlights In History" (a printed timeline) and other graphs and headings make it easy to find information.
The topics are written by various authors, who are cited at the end.