Bennett, P. A., Books and printing : A treasury for typophiles, 1991.

WWW VIAF, Dic. 26, 2016. Calkins, Earnest Elmo, 1868-1964. https://viaf.org/viaf/52930363/

Earnest Elmo Calkins (March 15, 1868 – October 4, 1964) was a deaf American advertising executive who pioneered the use of art in advertising, of fictional characters, the soft sell, and the idea of "consumer engineering". He co-founded the influential Calkins and Holden advertising agency. https://en.wikipedia.org/wiki/Earnest_Elmo_Calkins