HEWLETT PACKARD HP 21

Description

Brand: HEWLETT PACKARD
Model: HP 21
Type: Scientific RPN calculator
Picture: HP 21
Batteries: Battery pack
Lifetime: Introduced: 1975
Terminated: 1978
Notes: This calculator is the successor of HEWLETT PACKARD’s very first scientific calculator, the HP 35. Its siblings are the financial model HP 22 and the programmable model HP 25.

It has a slider to switch between DEGrees and RADians mode for the trigonometric functions.

Next to the quite common functions M+ and M− it adds two extra memory arithmetic functions M× and M÷.

For more information on this beauty please refer to the better sources, like The Museum of HP Calculators (link validated 2025-12-06). There is also information on this calculator on Wikipedia (link validated 2025-12-06)

Many thanks to Richard Pilkington of the University of Salford for donating this calculator to the museum.

Peripherals

A power adapter.


©2025 Ernst Mulder