HP21 scientific RPN calculator

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.
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What's New

Re-compiled to support Android 9
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Additional Information

Updated
May 7, 2019
Size
Varies with device
Installs
10,000+
Current Version
Varies with device
Requires Android
Varies with device
Content Rating
Everyone
Permissions
Offered By
Milan Cisár
Developer
Sebranice 240 Sebranice u Boskovic Czech republic
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