--- title: "RPN-55 SD - Reviews, Revenue and Downloads in United States | Apple App Store" description: "RPN-55 SD is the first photo-realistic simulation for the iPhone of Hewlett-Packard's low-cost alternative to the famous HP-65 programmable scientific calculator. Produced from 1975 through 1977, it w" --- # RPN-55 SD — United States > Classic HP Calculator w/Timer ![RPN-55 SD App Icon](https://is1-ssl.mzstatic.com/image/thumb/Purple211/v4/d7/f9/ac/d7f9ac73-f4a1-e1fc-8aff-bfef7d7ac58c/AppIcon-0-1x_U007emarketing-0-8-0-85-220-0.png/400x400bb.png) **Developer:** [Willy Kunz](https://apptail.io/developer/willy-kunz-XNx) (Switzerland) **Category:** Productivity **Rating:** 5.0/5 (8 ratings) **Price:** $1.99 **Bundle ID:** RPN-55-SD **Store:** Apple App Store **Country:** United States **Version:** 3.3 (released 2025-10-17) **Original Release:** 2019-07-03 **App Store Link:** [Download on Apple App Store](https://apps.apple.com/us/app/app/id1469907917) **AppTail Page:** [https://apptail.io/app/rpn-55-sd-rfhd/united-states](https://apptail.io/app/rpn-55-sd-rfhd/united-states) ## RPN-55 SD Description RPN-55 SD is the first photo-realistic simulation for the iPhone of Hewlett-Packard's low-cost alternative to the famous HP-65 programmable scientific calculator. Produced from 1975 through 1977, it was the "Merlin" member of the classic HP calculator series, priced at $395. HP claimed that it featured "(...) more pre-programmed functions than any other scientific pocket calculator in the world." A main feature of the HP-55 was a crystal-controlled 100-hr digital timer with the ability to store times while the timer was running and later recall them. On RPN-55 SD the timer may also act as a 12-hr or 24-hr clock, including date and weekday display. While the simulator works just like the original calculator – except being much faster and having twice the program memory – you can turn on extended features to make it even more enjoyable to use. RPN-55 SD comes complete with original HP programs built in. Features: • Photo-realistic look-and-feel • Vintage mode or Extended mode • Programmable (99 steps), conditional branching • Insert and delete steps with automatic address correction • Delete range of steps • Subroutines (4 levels) • 20 registers, "continuous", with unrestricted store/recall arithmetic • "Live" register view • Program listing view • Program library view • Store and retrieve any number of programs • 100-hr timer supporting 10 split times and 12/24-hr clock mode with date • Swap unit conversions with additional functions, e.g. hyperbolics • Sharing: e-mail, AirDrop, Dropbox, copy, paste, print • 112 programs pre-installed Calculator functions: • Statistics (linear regression, mean, standard deviation, correlation coefficient, x- and y-estimates) • Trigonometric functions (degrees, radians, grads) • Polar/rectangular conversions • Inverse, square root, logarithm, exponential, pi • Storage arithmetic (store and recall) • Percent, absolute, integer, fractional value, round • Factorial • Random number • Unit and hours conversions Details: cuveesoft.ch/rpn55 ## RPN-55 SD Screenshots - [Screenshot 1](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource221/v4/77/3f/7d/773f7d49-2152-eec8-9e9b-91d4de02dbc2/1.png/1242x2208.png) - [Screenshot 2](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource211/v4/73/9f/9f/739f9ffb-36f4-6b71-9595-2902ae779997/2.png/1242x2208.png) - [Screenshot 3](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource221/v4/f4/df/26/f4df26e6-fa90-971a-7947-3482641e3f1c/3.png/1242x2208.png) - [Screenshot 4](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource211/v4/6c/3a/28/6c3a2818-3fe2-5c4d-13f0-25b2a2ee31e5/4.png/1242x2208.png) - [Screenshot 5](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource211/v4/98/b1/78/98b17877-f023-39ce-5c9a-747edba9200e/5.png/1242x2208.png) - [Screenshot 6](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource221/v4/13/12/2a/13122af5-f436-ff5e-0024-bfa9980f4cb0/6.png/1242x2208.png) - [Screenshot 7](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource221/v4/dc/4e/ed/dc4eed49-a6a4-7cda-2956-d94583e7a227/7.png/1242x2208.png) - [Screenshot 8](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource211/v4/d9/0d/ee/d90dee26-f5d5-5a41-144f-ba0d96726ccd/8.png/1242x2208.png) - [Screenshot 9](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource211/v4/d5/12/d3/d512d32c-8d32-7510-c82c-fe44bc513a7a/9.png/1242x2208.png) - [Screenshot 10](https://is1-ssl.mzstatic.com/image/thumb/PurpleSource221/v4/87/4d/24/874d24dd-670e-0c4f-7b90-712251fad168/10.png/1242x2208.png) ## RPN-55 SD Rating Breakdown in United States - 5 stars: 8 (100%) - 4 stars: 0 (0%) - 3 stars: 0 (0%) - 2 stars: 0 (0%) - 1 stars: 0 (0%) ## RPN-55 SD Reviews in United States ### ***** "Love the newest version" I've been using this app for several years, it's my favorite calculator app by far. My only gripe was minor - when launching the app the image of the calculator would appear immediately but it took a few seconds before it would accept keystrokes. So I would hit buttons but they wouldn't register, a bit frustrating. If you just leave the app running in the background that's not an issue, the calculator is instantly ready to go when you bring it to the foreground. But I'm in the (bad?) habit of closing apps after I'm done with them so I have to relaunch it every time I need it. Leftover habit from the 1970s when you had to live with 4K of RAM in your 8080 micro computer... The new version is much much quicker to launch and completely solves the lost keystrokes problem. A great improvement for old geezers like me. Thank you! -- Dana1824, 2025-09-07 ### ***** "Hyperbolic functions" In the next update for this calculator please add the six hyperbolic functions. HSIN, HCOS, HTAN, ARCHSIN ARCHCOS, ARCHTAN. This is a five star appreciation. -- challah nibler, 2023-06-29 ### ***** "My Calculator of Choice" The HP 55 was my first scientific calculator. It got me through high school physics and an electrical engineering degree at UC Berkeley. (I used a Pickett N-500-ES slide rule for high school chemistry.) These days, the RPN-55 app is my calculator of choice. It provides all the functions I tend to need, packaged in a way that brings back pleasing memories from decades ago. In terms of function, the standard HP 55 H.MS± functions are surprisingly useful (on occasion), and I don't "Replace Unit Conversions" because I find the unit conversions more nostalgic and useful. In a future release, it would great to have the "high contrast mode" feature implemented (such as in RPN-25 CE). You might imagine that my eyes have aged somewhat since my time with the physical HP 55, and any help would be appreciated! Even better would be an HD edition which can display the stack and registers (as in RPN-45 HD). But in its current incarnation, RPN-55 is eminently functional and fun to use. -- dmng, 2022-07-22 [View all RPN-55 SD reviews and detailed analytics on AppTail](https://app.apptail.io/signup?utm_campaign=ai-crawl&utm_content=reviews) ## Apps Similar to RPN-55 SD - [iHP48](https://apptail.io/app/ihp48-jRx/united-states) - [WP 34s](https://apptail.io/app/wp-34s-nRlc/united-states) - [RLM-15CX](https://apptail.io/app/rlm-15cx-xPxc/united-states) - [i41CX+](https://apptail.io/app/i41cx-blzc/united-states) - [i41CX](https://apptail.io/app/i41cx-tOLc/united-states) - [RLM-17BX](https://apptail.io/app/rlm-17bx-uLUc/united-states) - [RLM-19BX](https://apptail.io/app/rlm-19bx-SDyj/united-states) - [DB48X](https://apptail.io/app/db48x-fTUq/united-states) - [DB50X](https://apptail.io/app/db50x-IHYq/united-states) - [DB40X](https://apptail.io/app/db40x-bNZq/united-states) ## RPN-55 SD Available In - [United States](https://apptail.io/app/rpn-55-sd-rfhd/united-states) - [Germany](https://apptail.io/app/rpn-55-sd-rfhd/germany) - [China](https://apptail.io/app/rpn-55-sd-rfhd/china) - [Brazil](https://apptail.io/app/rpn-55-sd-rfhd/brazil) - [France](https://apptail.io/app/rpn-55-sd-rfhd/france) - [Mexico](https://apptail.io/app/rpn-55-sd-rfhd/mexico) - [Brunei](https://apptail.io/app/rpn-55-sd-rfhd/brunei) - [Belarus](https://apptail.io/app/rpn-55-sd-rfhd/belarus) - [Canada](https://apptail.io/app/rpn-55-sd-rfhd/canada) - [Switzerland](https://apptail.io/app/rpn-55-sd-rfhd/switzerland) - [Chile](https://apptail.io/app/rpn-55-sd-rfhd/chile) - [Colombia](https://apptail.io/app/rpn-55-sd-rfhd/colombia) - [Cyprus](https://apptail.io/app/rpn-55-sd-rfhd/cyprus) - [Czechia](https://apptail.io/app/rpn-55-sd-rfhd/czechia) - [Denmark](https://apptail.io/app/rpn-55-sd-rfhd/denmark) - [Dominican Republic](https://apptail.io/app/rpn-55-sd-rfhd/dominican-republic) - [Algeria](https://apptail.io/app/rpn-55-sd-rfhd/algeria) - [Ecuador](https://apptail.io/app/rpn-55-sd-rfhd/ecuador) - [Estonia](https://apptail.io/app/rpn-55-sd-rfhd/estonia) - 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[Australia](https://apptail.io/app/rpn-55-sd-rfhd/australia) - [Azerbaijan](https://apptail.io/app/rpn-55-sd-rfhd/azerbaijan) - [Belgium](https://apptail.io/app/rpn-55-sd-rfhd/belgium) --- ## About AppTail [AppTail](https://apptail.io) is a mobile app intelligence platform providing app analytics, ASO (App Store Optimization) tools, keyword tracking, competitor analysis, revenue estimates, and review monitoring for iOS App Store apps. 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