Little Duke © 1932 O.D. Jennings.
Machine's picture.
Collector's Treasury of Antique Slot Machines from Contemporary Advertising - Peter Bach - Page 72 & 73
For Amusement Only - Thomas Gustwiller - Taylor Printing - 1995 - Page 34
The Coin Machine Journal - January 1940 issue
Automatic Pleasures - The History of the Coin Machine - Nic Costa - 1988 - Page 68