RPN vs PDF Flatten
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
RPN
This app emulates the first pocket scientific calculator, offering a photo-realistic vintage experience. It simulates original operating speeds and unique arithmetic bugs, with optional modern enhancements like non-volatile registers.
- Photo-realistic look-and-feel
- Multiple vintage skins
- Vintage and Enhanced modes
- Optional key-click and key-glow
- Swipe to correct input
- Display stack and memory registers
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On January 4, 1972, Hewlett-Packard announced the HP-35, world's first scientific calculator small enough to fit in a pocket - more precisely, Bill Hewlett's shirt-pocket. The HP-35 was an immediate hit with students, engineers, and scientists. Despite its steep price of $395 (about $3000 today), it sold ten times better than anticipated in the first year. Experience this unique calculator that won HP the prestigious "IEEE Milestone in Electrical Engineering and Computing" in 2009. Features: • Photo-realistic look-and-feel • Three skins: version 1, versions 2 & 3 (1973) and final version 4 (1974) • Vintage mode and Enhanced mode • Key-click and key-glow, both optional • Swipe left across display to correct number input errors • Cut/copy/paste display value • Display stack registers and memory registers • All decimal points but one light when iPhone battery charge drops below 5% Vintage mode In this mode, peculiarities of a real HP-35 are simulated: - original speed of operation - stack register Z copied to T on trig functions - leading zeros may be entered; zero can be made negative - a negative number may be entered by pressing CHS before or after the number - a keyboard entry or RCL immediately following STO does not raise the stack - for version 1 only: simulation of a number of known arithmetic bugs Enhanced mode - non-volatile stack and registers - use registers 1 through 9 with HP-45-like register arithmetic - register 0 works as LastX register
PDF Flatten
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Turn fillable PDF forms into static, non-editable PDFs fully offline. PDF Flatten converts interactive PDF forms (AcroForms) into static documents that can no longer be edited. Perfect for official forms, contracts, and secure document submissions. No subscriptions. No accounts. No uploads. Everything is processed directly on your device. Why use PDF Flatten? • Convert fillable PDF forms into static PDFs • Remove interactive fields permanently • Works offline and fully private • No watermark • Fast native performance • Simple and clean interface Perfect for: • Contracts and agreements • Business forms • School documents • Applications and paperwork • Any fillable PDF form How it works: 1. Select a fillable PDF 2. Tap Flatten 3. Save or share your static PDF That is it. Your documents never leave your phone. Simple. Secure. Offline.
Screenshots
Verdict
The clearest difference is chart position: PDF Flatten at #198 against RPN's unranked. PDF Flatten also leads on price ($0.99 vs $1.99). RPN's advantage is iOS requirement (12.0 vs 15.1). On ads, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
RPN costs $1.99 and PDF Flatten $0.99 up front. Neither carries in-app purchases, so what you see is what you pay.
| Parameter | RPN | PDF Flatten |
|---|---|---|
| Price | $1.99 | $0.99 — better |
| Rating | 4.4 (14 ratings) — better | — |
| Positive reviews | 71.4% of reviews | — |
| Number of ratings | 14 — better | — |
| Update frequency | Every 6 months | — |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | — |
| Best chart rank | — | #198 — better |
| Devices | iPhone, iPod | iPhone, iPad, iPod — better |
| Requires iOS | 12.0 — better | 15.1 |
| Further details — not scored | ||
| Size | 14 MB | 29 MB |
| Age rating | 4+ | 4+ |
| Developer | CuVee Software | StudyBridge LLC |
In-app purchases
RPN
No in-app purchases
PDF Flatten
No in-app purchases









