# HP-35 — RPN Calculator. HP-35, 45, 21

> Emulates classic Hewlett Packard RPN scientific calculators. (iPhone/iPad app by Enrique Haro.)

- Source: https://appshunter.io/ios/app/hp-35/id6738010641 (this page in markdown: same URL + `.md`)
- Developer: [Enrique Haro](https://appshunter.io/developer/1778874870)
- Category: Utilities, Productivity
- Price: Free
- Rating: 5.00/5 from 5 App Store ratings · 3 written reviews indexed
- Age rating: 4+
- Requires: iOS 17.2 · 2 MB
- Languages: American English
- Released: 2024-11-13
- Data updated: 2026-08-17
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/hp-35/id6738010641/reviews.md

## What is HP?

The classic Hewlett Packard RPN (Reverse Polish Notation) calculators.
- HP-35, HP-45. First pocket scientific calculators (1972). 
- HP-21. 2nd gen of the HP-35 (1975)

## Key features

- RPN calculator emulation
- HP-35 model
- HP-45 model
- HP-21 model
- Classic scientific calculator interface

## Recent user reviews (3 of 3)

All indexed reviews: https://appshunter.io/ios/app/hp-35/id6738010641/reviews.md

### 5/5 — Excellent interpretation

*2025-11-27*

This is an easy to use interpretation of the HP’s ground breaking RPN calculator. Love the HP 45 with the % key. Great job and highly recommended.

### 5/5 — It’s a match!

*2025-05-21*

This is a great RPN calculator and an accurate representation of the original model. I would recommend it!

### 5/5 — Looks like the original!

*2025-03-11*

Great design and works just like the model I was looking for!

## Frequently asked questions about HP

### What calculators does HP-35 emulate?

HP-35 emulates the classic Hewlett Packard HP-35, HP-45, and HP-21 RPN calculators. These were among the first pocket scientific calculators released in the 1970s.

### Is HP-35 free to use?

Yes, HP-35 is completely free to download and use. It does not require any payment or in-app purchases.

### What devices does HP-35 support?

HP-35 is currently supported on iPhone devices. It is designed for the iOS mobile operating system.

### How often is HP-35 updated?

The latest version, 2.6, was released on March 22, 2026. While the last update date is in the future, indicating ongoing development, users can expect updates to maintain compatibility and potentially add features.

### What is the user rating for HP-35?

HP-35 has an excellent rating of 5.0 stars based on 5 user reviews. This indicates a very high level of user satisfaction.

### Does HP-35 have ads?

No, HP-35 does not contain advertisements. Users can enjoy an ad-free experience while using the calculator.

### What is Reverse Polish Notation (RPN)?

Reverse Polish Notation (RPN) is a mathematical notation where every operator follows all of its operands. This differs from the more common algebraic notation and is a key feature of the emulated HP calculators.

### What is the age rating for HP-35?

HP-35 has an age rating of 4+. This means it is suitable for users of all ages, with no content restrictions.

## Version history (last 5 releases)

### 2.6 — 2026-03-22

Minor Improvements and bug fixes

### 2.5 — 2026-03-20

- Fix the cms/inch, kg/lb, ltr/gal conversion in the HP-45
- Disabled the MK-61 until the full implementations is reviewed

### 2.3 — 2025-08-06

Fix for crash in Double to Int conversion

### 2.2 — 2025-08-05

Improved layout in iPad and iPhone SE

### 2.1 — 2025-07-31

New Model Selection view. Expect new stuff here
Added a display blink when clicking ENTER for a better visual experience

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## More apps by Enrique Haro

- [RepubliCal](https://appshunter.io/ios/app/republical/id6744465767)

All apps by Enrique Haro: https://appshunter.io/developer/1778874870

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-17.*