The New HP-21 Scientific Pocket Calculator | 102646261 | Computer History Museum
HP-21 Inside
HP-21 - Wikipedia
HP Woodstock
Hewlett-Packard HP-21 Handheld Electronic Calculator | National Museum of American History
Hewlett Packard security cradle to HP 21 22 25 25C 27 29C Calculator 1970 USA - Vintage Man Stuff
File:Vintage Hewlett-Packard Model 21 Electronic Pocket Calculator, Made in the U.S.A., A Scaled-Down HP 25, Circa 1975 (11574422413).jpg - Wikimedia Commons