Join or Sign In

Sign in to add and modify your software

Continue with Facebook Continue with email

By joining, you agree to our Terms of Use and acknowledge the data practices in our Privacy Policy.

HP21 scientific RPN calculator for Android

By Milan Cisr Free

Developer's Description

The HP-21 was a scientific calculator produced by Hewlett-Packard between 1975 and 1978. It was designed as a replacement for the HP-35, and was the first from so called Second Generation Handheld Calculators.

As with most HP calculators then and now, the HP-21 used RPN entry logic, with a four-level stack. It also had a single user-accessible memory register. A shift key provided access to functions whose legends were printed on the fronts of the tall trapezoidal keys.

To enhance practical usability, display was modified to show both X and Y register. Also I have eliminated mechanical DEG/RAD switch and moved the function under DSP button.

HP21 has few big enough buttons to be used comfortably on mobile devices.

Full Specifications

What's new in version 2.9


Release July 18, 2019
Date Added July 18, 2019
Version 2.9

Operating Systems

Operating Systems Android
Additional Requirements Requires Android


Total Downloads 13
Downloads Last Week 3
Report Software

Related Apps

Gboard - the Google Keyboard

Gboard - the Google Keyboard



VPN Free - Betternet Hotspot VPN & Private Browser

VPN Free - Betternet Hotspot VPN & Private Browser

VPN by Private Internet Access

VPN by Private Internet Access

Best VPN Services for 2021

Best for privacy

3 months free with 1-year plan

Best for customer support

$39.99 for the first 12 months

Best for zero logs

$4.87.99/months for a 1-year plan

Best money-back guarantee

$2.99/months for a 3-year plan