Download HP21 scientific RPN calculator apk 2.4 free for Android smartphone

29 Feb
HP21 scientific RPN calculator

Posted by Milan Cisár in Tools | Feb. 29, 2016 | 5 Comments

Apk file size: 2.2 MB

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.

Whats new

    To improve usablity now running in full screen.

Milan Cisár part of our Tools and have average installs from 1000 to 5000. Last Update Feb. 29, 2016. Google play rating is 86.9231. Current verison is 2.4. Actual size 2.2 MB.

Download hp21-scientific-rpn-calculator.apk 2.2 MB

5 Comments

Eric Huerta

The keypad is very responsive, the two levels of the stack that are always visible are very helpful. The implementation of this venerable HP design on Android rocks, because the functionality is basic enough for quick occasional calculations, there is nothing more but an efficient and very handy calculator machine at hand all the time with you, no nag screen, no intention to push it on you to force you to pay, awesome. The only thing that needs some work is the high battery consumption.

Eric Katz

Bug Starting new entry with . does not copy x into y register. Need to preceed the . with a zero. This is a bug.

Eric Huerta

RPN at its best and always handy. The keypad is very responsive, the two levels of the stack that are always visible are very helpful. The implementation of this venerable HP design on Android rocks, because the functionality is basic enough for quick occasional calculations, there is nothing more but an efficient and very handy calculator machine at hand all the time with you. Only "bug" is that typing (EXX) (3) (Enter), for example, does not input 1000 as with most HPs. I hope the author fix this soon.

Mister Neutron

Beautiful on small screen devices I love Free42, but sometimes I just want a classic bare bones four-banger plus basic scientific RPN calc. This is a great alternative. And the display of X /and/ Y is both useful and historic: Early HP desk calculators did it. Well done!

KW Chan

Upon startup, it returns to the default three decimal places and cannot turn off keypad vibration

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