GO-21 SciRPN simulates the venerable HP-21 Pocket Scientific Calculator from 1975. Virtually indistinguishable from the real item in operation, GO-21 is a powerful yet simple retro calculator.

GO-21 combines the classic behavior of the HP-21 with modern iPhone capabilities like key click sounds, visual touch feedback, persistent stack, memory and display format, and help information.

• Requires iOS 8.0 or later
• Copy / Paste
• Shake to clear X
• Swipe gestures that roll and display the stack
• Addition, subtraction, multiplication, division
• Trigonometric functions : sin, cos, tan, sin⁻¹, cos⁻¹, tan⁻¹, degrees or radians
• Rectangular/polar coordinate conversion
• Logarithmic functions : log, 10**x, ln, e**x
• Other functions : Y**x,1/x, √x, π
• Display : LED, 10 significant digits (8 + 2 digit exponent in scientific notation), 10-99 to 10+99
• Memory : 4 register stack, stack roll down, X-Y interchange, manual memory with register math
• floating stack and memory window

What’s New

Version 4.13

- Update for iOS 12.0.
- Do not raise the stack when using the EEX shortcut immediately after an ENTER.

Ratings and Reviews

5.0 out of 5
6 Ratings
6 Ratings
NanoRon ,

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.

lbartosh ,

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.

Noneblank Nickname ,

Return with us now to the days of yesteryear

I bought an HP-21 during my third semester of college in 1976. At that time they were still teaching students how to use a slide rule.

The app is a very good reproduction of the HP-21's look and functions/functionality. I has the functions I want and doesn't have a lot of functions that I don't use. It has a useful Help file.


Technology Man IR
26.5 MB
Requires iOS 8.0 or later. Compatible with iPhone, iPad, and iPod touch.
Age Rating
Rated 4+
Copyright (©) 2009 - 2018 Stephen O. Lidie, All rights reserved.


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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