GO-21 SciRPN

GO-21 SciRPN

by Steve Lidie

12 ratings
17 reviews
$2.99

Details

  • Released
  • Updated
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About

This app faithfully recreates the 1975 HP-21 pocket scientific calculator, offering RPN functionality and a full suite of mathematical, trigonometric, and logarithmic functions. It features a 10-digit LED display, stack and storage registers, and a keystroke log for detailed operation tracking.

RPN (Reverse Polish Notation)
10-digit LED calculator display
Four stack registers with roll down
One storage register
Math, trigonometric, logarithmic functions
Keystroke log
Copy/Paste display functionality
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What's New in GO

26.5.1

June 11, 2026

- Repair broken icon and update documentation. - Update to Apple OS versions 26.5.1.

User reviews

Hp-21 a constant companion !

I bought my HP-21 shortly after i saw it in Machine Design magazine in 1976. From then on it became my constant companion until appx 1995 or so when it gave up the ghost and would no longer illuminate. Much later on I was overjoyed to find an e-version replica of my faithful pocket resource, though he was no longer needed after I retired from field work. Today I have switched to Android apps and regret that I cannot find a replica of this trusty device,,,,, and would like to ask IF THERE IS ONE (?) or one under development? All iOS products havre become too expensive and unreliable !
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50 years later - Thank you

Many thanks for giving me the opportunity to use this RPN calculator. I bought my very first HP 21 C in 1972 when studying at Polytechnic School of Cameroon. 50 years later, I am still very happy and proud using RPN devices and programming Common LISP.

Hate that high visibility setting

To me, the value of this app (and all the other RPN apps that I have) is the authenticity of them. Otherwise, there are a gazillion calculators with different sized displays out there with RPN.

Instead of making the X view high visibility, why not enlarge the calculator itself to be full screen (even getting rid of the stack view optionally)

Then I’ll go back to 5 stars again which otherwise this app absolutely deserves.
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Response from developer

For some thoughts on sizing, see: https://www.bigcatos.com/BigCatOs/go-2x-scirpn/go-21sizehistory.html The App seems to be sized as authentically as possible. The stack view is and always has been optional, simply hide it forever, as described in the documentation. The High Visibility Display setting is optional and disabled by default so you never have to see it, thus the calculator remains in its pristine state. This option has been requested by two groups of users: as an Accessibility assist for those with diminished vision, and folks who use the App outdoors as part of their work.

Lean & Mean

I’ve been using this app for a number of years and have been very satisfied and figured it was time I gave it a review. As an engineer, I loved my HP-21 and was sad when it finally died many moons ago. I searched and searched for a simple reverse Polish calculator app, but could never find a good one. This is a good one. A clean but elegant emulation of a classic design. Highly recommended.
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My thoughts on the HP 21 app

I have an hp 21 that we purchased new and I've always loved it, not only for the RPN feature but for the simplicity. This is such a nice app for anyone familiar with the HP line plus it shows the stack. Highly recommend.

Developer apps

FAQ

What is GO-21 SciRPN?

GO-21 SciRPN is a mobile application that simulates the operation of the classic HP-21 pocket scientific calculator from 1975. It offers a faithful recreation of its interface and functionality, including Reverse Polish Notation (RPN).

What functions does GO-21 SciRPN offer?

GO-21 SciRPN provides a comprehensive set of functions including math, trigonometric, polar/rectangular conversions, logarithmic, and power functions. It also features four stack registers and one storage register for calculations.

Does GO-21 SciRPN have ads?

No, GO-21 SciRPN is ad-free. The application is a paid utility designed for a focused user experience without advertisements.

What devices does GO-21 SciRPN support?

GO-21 SciRPN is available on a wide range of Apple devices, including iPhone, iPad, iPod, Mac, and Apple TV. This broad compatibility ensures users can access it across their ecosystem.

How often is GO-21 SciRPN updated?

The latest version, 7.1, was released on September 17, 2024. Updates are provided periodically to maintain compatibility and performance on supported devices.

What is the price of GO-21 SciRPN?

GO-21 SciRPN is a paid application, available for $2.99. This one-time purchase grants access to all its features without further in-app purchases or subscriptions.

What is Reverse Polish Notation (RPN)?

Reverse Polish Notation (RPN) is a mathematical notation where every operator follows all of its operands. GO-21 SciRPN utilizes this method, which is a key feature of the HP-21 calculator it emulates.

What is the age rating for GO-21 SciRPN?

GO-21 SciRPN has an age rating of 4+. This indicates it is suitable for users of all ages, with no mature content.