HP-21 scientific calculator | X1405.97 | Computer History Museum
HP Woodstock
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
Hewlett Packard HP-21 Calculator Only - TESTED | eBay