![File:Vintage Hewlett-Packard Model HP-38C Electronic Programmable Pocket Calculator, Red LED Display, Sealed Battery Pack, Made In USA, Circa 1979 (33442456024).jpg - Wikimedia Commons File:Vintage Hewlett-Packard Model HP-38C Electronic Programmable Pocket Calculator, Red LED Display, Sealed Battery Pack, Made In USA, Circa 1979 (33442456024).jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/2/22/Vintage_Hewlett-Packard_Model_HP-38C_Electronic_Programmable_Pocket_Calculator%2C_Red_LED_Display%2C_Sealed_Battery_Pack%2C_Made_In_USA%2C_Circa_1979_%2833442456024%29.jpg)
File:Vintage Hewlett-Packard Model HP-38C Electronic Programmable Pocket Calculator, Red LED Display, Sealed Battery Pack, Made In USA, Circa 1979 (33442456024).jpg - Wikimedia Commons
![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 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](https://upload.wikimedia.org/wikipedia/commons/a/af/Vintage_Hewlett-Packard_Model_21_Electronic_Pocket_Calculator%2C_Made_in_the_U.S.A.%2C_A_Scaled-Down_HP_25%2C_Circa_1975_%2811574422413%29.jpg)
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
![File:Vintage Hewlett-Packard Model HP-45 Advanced Scientific Pocket Calculator, HP's Third Handheld Electronic Calculator, Introduced in 1973 and Discontinued in 1976 (11590594223).jpg - Wikimedia Commons File:Vintage Hewlett-Packard Model HP-45 Advanced Scientific Pocket Calculator, HP's Third Handheld Electronic Calculator, Introduced in 1973 and Discontinued in 1976 (11590594223).jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/5/5a/Vintage_Hewlett-Packard_Model_HP-45_Advanced_Scientific_Pocket_Calculator%2C_HP%27s_Third_Handheld_Electronic_Calculator%2C_Introduced_in_1973_and_Discontinued_in_1976_%2811590594223%29.jpg)
File:Vintage Hewlett-Packard Model HP-45 Advanced Scientific Pocket Calculator, HP's Third Handheld Electronic Calculator, Introduced in 1973 and Discontinued in 1976 (11590594223).jpg - Wikimedia Commons
![File:Vintage Hewlett-Packard Model HP-45 Advanced Scientific Pocket Calculator, HP's Third Handheld Electronic Calculator, Introduced in 1973 and Discontinued in 1976 (38772251491).jpg - Wikimedia Commons File:Vintage Hewlett-Packard Model HP-45 Advanced Scientific Pocket Calculator, HP's Third Handheld Electronic Calculator, Introduced in 1973 and Discontinued in 1976 (38772251491).jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/1/1c/Vintage_Hewlett-Packard_Model_HP-45_Advanced_Scientific_Pocket_Calculator%2C_HP%27s_Third_Handheld_Electronic_Calculator%2C_Introduced_in_1973_and_Discontinued_in_1976_%2838772251491%29.jpg)