42s RPN Calculator 4+

Byron Foster

    • 4.0 • 27 Ratings
    • $4.99

iPhone Screenshots


42s is an iPhone port of Thomas Okken's excellent and stable Free42, a complete re-implementation of the highly praised HP-42S RPN calculator. There are no ROMs or emulators involved allowing 42s to run natively and fast. This calculator provides all the functionality of the original 42S with several hundred functions, programability, printer output, etc. Additionally, several enhancements have been made over the original calculator such as additional precision and the ability to import and export programs.

Features include:

* Programmable for custom functionality. Packages are available for additional functionality including Engineering, Scientific, Financial, Statistical, etc. Backward compatible with 41CX programs.
* Internally stores values and performs operations in 25 digit decimal precision.
* Use the iPhone keyboard for entering character data, or variable names.
* Runs several orders of magnitude faster then the original calculator, including program execution, solving, integration, matrix operations, etc...
* Swipe LCD vertically to get up to 7 lines of display.
* Double tap LCD to cut and paste one or more numbers from the stack, or paste one or more numbers to the stack
* swipe LCD vertically on the right hand side to roll stack contents, or to scroll a program in program mode.
* Sound tones mimic those of the original HP-42S
* Double tap print output view to copy print contents
* Display last x register in the upper right hand corner of LCD
* Tap LCD in alpha entry mode to toggle the display of the iPhone keyboard.
* Added option for a dynamically sized stack. Choose between the traditional (X, Y, Z, T) style stack, or a fully dynamic stack.
* Added option for no stack lift on Enter.
* Added DROP command, executed by doube tapping the back key
* Added option to remove device status bar for a larger LCD
Added additional lines to LCD modes, now supports up to 6 lines of stack, or 7 lines of program.
* Added scroll bar to program mode.
* Program mode can now be scrolled with the menu active.
* Import/Export functions.

Added in 3.0:

* Compatibility with iOS4 including application switching and compatibility bugs
* Added hi-rez (retinal) key pad image for iPhone 4
* Added Undo and Redo functions for the stack. Swiping the LCD left or right performs these operations.
* Added display option to show flags 0-4 at the top of the display if they are set.

What’s New

Version 3.2.3

This app has been updated by Apple to display the Apple Watch app icon.

Fixed screen scaling for larger devices

Ratings and Reviews

4.0 out of 5
27 Ratings

27 Ratings

dsbushy ,

Opens then disappears

Fantastic app! I’ve been using it almost daily for years with programs I’ve written. Can’t work without it.
Now with the iOS 14.2 update it will open and then immediately disappears
Hopefully this program is still supported

CalcFreak ,

By far the best scientific calculator

I just wanted to update my review. Conclusion: I still love this thing. I own two real 42S calculators, and the one from Switzerland (DM42), but this is the best because I always have my phone handy, and the extensions to the original are well thought out.

I love this thing. I collect calculating machines of various kinds - from Sorobans and Napier’s Bones to slide rules and mechanical calculators to electronic calculators, and this is my favorite on my phone. And the only one that merits a top level spot on the first page of apps.

7738+u!7) ,

Prefer the prior version

Love the calculator as a whole. Best RPN calculator I have found on the iPhone. Great recreation of the classic HP 42s.

I'm not fond of the new updates, however. My review reflects the recent update only. I updated to the latest version and wish that I had not. On iPhone 6s the calculator is shifted to the top of the phone screen leaving a large blank space below it. The actual calculator size is no bigger on the screen than it was with the prior version, and with the prior version, it was centered more attractively and easier to reach with my fingers. Update, provided no known advantage for me.

App Privacy

The developer, Byron Foster, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

You Might Also Like