Site menu Touch 15i: the scientific calculator for iPhone and Android
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Touch 15i: the scientific calculator for iPhone and Android

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Figure 1: Touch 15i screenshot - iOS

Figure 2: Touch 15i screenshot - Android

Touch 15i is a scientific calculator for Android and iOS that implements most functions of the HP-15C.

Get it on Google Play

Get it at App Store

Emulators of Hp-1xc RPN calculators by EPx

Figure 3: Some user reviews

Touch 15i uses the same base engine of the HP-15C Web emulator. It aims to mimic all features (and limitations) of the real device.


The calculator mimics the 15C calculator quite closely. It shares the same limitations as an original 15C: 322 programming steps, 66 memory positions etc.

Differences from real calculator

Figure 4: Touch 15i screenshot

First of all, it is important to mention that the calculator engine does not use a ROM dump. It is a clean-room implementation. So the results simply can not guaranteed to be exactly equal:

Saving copies of the memory

The app allows to store and retrieve copies of the memory. This is especially useful to have many different programs available and ready to use (perhaps the programs would not fit in the memory all at once, or it is simply inconvenient to have them all in the same memory image). In any case, the whole memory, including all registers and configurations, is saved along with the program.

Saving copies of the memory in iPhone

Use the following key combinations to access this feature: The memories are stored locally as well as in iCloud. If you have configured iCloud in your devices, you can transfer memories between devices, provided that they are configured with the same iCloud account. Also, a new device will have access to the previously saved memories, so you don't lose anything when you exchange your iPhone for another one.

Differences in advanced operations

Some differences are more subtle, they affect only advanced operations and they take a longer explanation.

Integration strategy. This calculator employs the Adaptive Simpson integration technique. It may and will return results very different from HP-15C when integrating "funny" functions e.g. with extreme values or extreme slopes.

Integration precision. When the display is in FIX mode, e.g. FIX 3, HP-15C integrates with precision 0.001 (regardless of how small or how big the results are). In the other hand, if display is in SCI mode, it integrates with 3 digits of precision. This implementation always follows the SCI criteria, so FIX 3 and SCI 3 yield the same precision: three significant digits.

Equation solving. This implementation tries to offer root-finding capabilities that are equal or better than HP-15C's, but it is expected that performance and results will be very different, at least for "difficult" functions. In some cases, this calculator will fare better; in other cases, the HP-15C will.

Matrix operations. Operations involving ill-conditioned or near-singular matrixes may return different values compared to HP-15C or to other matrix-solving software. Two factors play a role here: this calculator uses 15-digit precision internally (more than HP-15C), and algorithms like matrix inversion and LU decompositon can be implemented in many different ways.

In particular, HP-15C guarantees to find an inverse for every square matrix, by doing small changes in values. This allows for operations with near-singular matrixes where the limited floating-point precision might be a problem. But the "tweaking" of matrixes is certainly made differently in each calculator, thus yielding different results.

Complex operations. Some operations in complex plane e.g. trigonometric and hyperbolic functions can be executed in many different ways. This calculator may show different results compared to HP-15C or to other software that can handle complex numbers, in particular when precision takes a role e.g. when the logarithm of a very small number is taken.

Touch the right upper corner of the screen to open a quick guide for some operations of the calculator:

Figure 5: Touch15i quick guide

Touch the upper left corner to copy the displayed value (the X register) to the clipboard. The value is copied in a "spreadsheet-friendly" or "data entry-friendly" format, that is: no thousand separators and point as decimal separator.

Settings (iPhone version)

This app adds a panel to device Settings. There, you can toggle decimal point as comma and keypress sound. These items may also be configured within the application screen, using the following 'apocryphal' key sequences:

In Android, the app implements a menu that is accessible via the Android-standard menu soft button, or by touching the upper left part of the screen, or by keying RCL g EEX.

Terms of use

The calculator is offered "as is". There are no guarantees of precision, exactness, or aplicability to any given purpose. The developer has no responsability for any damages incurring from usage of this software.

Privacy policy

The app does not send any user data to any remote party, and it does not share data with other apps.

In Android, when the user saves copies of the memory, they are written as files in the "storage area". Files in this area can be manipulated by any other app installed on the same phone. If this is a problem, remove these files from the SD Card once they fulfill their intended usage.


You can use the Market support tools, or the comment section at this page, or contact me by e-mail if you have any issues or feedback.

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