APA-referens (7:e uppl.)

Clapp, F. L., & Huebner, B. P. (1924). The number combinations, their relative difficulty and the frequency of their appearance in text-books.

Chicago-referens (17:e uppl.)

Clapp, Frank L., och Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. Madison, Wis, 1924.

MLA-referens (8:e uppl.)

Clapp, Frank L., och Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. 1924.