Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
RPN 28x Calc is a programmable scientific calculator with a pleasingly classic look
$6.99 · In-app purchases
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
A product spec, screen plans, and build steps for your coding agent.
First kit free with a verified email
Combine features and design from your favorite apps.
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Generating… usually about a minute.
What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
A product spec, phased build plan, differentiation notes, and screen references.
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Goal: Send a clear invoice after finishing a job.
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
Rork plan preview for RPN 28x Calc: map the core Productivity workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Assumption to check: Limited customization options for users
Validate with people who use this workflow before building.
Hypothesis 2
Assumption to check: No support for complex scientific functions
Validate with people who use this workflow before building.
Hypothesis 3
Assumption to check: History can become cluttered
Validate with people who use this workflow before building.
Hypothesis 4
Assumption to check: No tutorial for new users
Validate with people who use this workflow before building.
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
RPN 28x Calc is a programmable scientific calculator with a pleasingly classic look. Despite its nostalgic appearance, it offers a modern and intuitive user experience, allowing you to interact with your operands by touching them in the display. It is a reverse-polish notation (RPN) calculator with a dynamic stack display. As you add more values to the stack, the display shown on an iPad automatically expands. To see more lines, simply swipe to scroll. You can also re-order the levels or modify any of the values on the stack. ----- "It’s the third RPN calculator I buy for my iPad 2 and the first that makes me happy. It’s graphically appealing, intuitive and very responsive. I rated it 5 stars." (Nuno Gomes) ----- Advanced commands are available in a secondary panel on iPad or as alternative button pages on iPhone. The buttons are efficiently grouped into five pages that you can quickly access by swiping left or right: - user-defined buttons, - letters A-Z for typing, - trigonometric, logarithmic, and data manipulation commands, - statistics, storage and programming commands - binary integers, system flags and boolean logic. This is why RPN 28x Calc is unique in its class: - You can tap a row to select it and issue commands for the selected level. - In REORD mode, it is possible to rearrange the stack by dragging the rows. - You can swipe up or down the display to see all levels. - When you enter a value, you can tap a digit to reposition the cursor. - Tap on the status indicators in the top of the display to change their state. - Drag buttons to re-arrange them as you like it (enable that in the settings). Additionally, on iPad: - The display automatically resizes to show more than just 4 levels of the stack. - You can slide the secondary panel out of view or swipe across the panel to navigate between button pages. New: - 147 scientific units and elementary physical constants. - Upper-tail probablity distribution commands. - Interactive program debugging. RPN 28x Calc is all you need. - High precision arithmetics. - Supports multiple data types: real numbers, complex numbers, binary integers, or lists, arrays, vectors, matrices, programs, names, and strings. - Name your own variables; inspect them in the variable viewer. - Use the rich command set to write your own programs. - Create buttons for your programs. - Interactive button reordering. - Browse all scientific units and constants in the units viewer. - View the command history and the results in the log viewer. - Customizable button click & alert volumes. - Support for landscape orientation. - Optional thousand separators. - Haptic feedback on iPhone. - External keyboard support. - Dark Appearance since iPadOS 13 or iOS 13. - Alternative, dark app icon. - Use the same app on iPad or iPhone. - Use the calculator in iPad multitasking, i.e. in a Slide Over view or in Split View. - No ads, no tracking, and no rating requests. - Downloadable user guide with introduction and command reference (PDF). ----- Plans for future versions (NOT YET SUPPORTED): - Arithmetic expressions.
Written user reviews are not shown here. Check current App Store reviews >
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.