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.
App Overview
RPN-65 SD
World's first pocket computer! Now running on your iPhone.
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
8 ratings · Top 5%
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.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
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.
Differentiate and validate
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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Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for RPN-65 SD: 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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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
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
Provide an easy way to access and manage past calculations.
Assumption to check: Limited calculation history view
Validate with people who use this workflow before building.
Hypothesis 2
Include more functions like trigonometric and logarithmic calculations.
Assumption to check: No support for advanced functions
Validate with people who use this workflow before building.
Hypothesis 3
Allow users to customize the interface and themes.
Assumption to check: Lack of customization options
Validate with people who use this workflow before building.
Hypothesis 4
Provide tutorials or tooltips to help users understand RPN.
Assumption to check: Steep learning curve for new users
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
World's first pocket computer! Now running on your iPhone. RPN-65 SD is the iPhone version of RPN-65 Pro, the first complete simulation of Hewlett-Packard's stunning HP-65 programmable calculator for iOS. Produced from 1974 to 1977 at an initial price of $795 (that's close to $5,000 today!), the HP-65 was a breakthrough. Not only was it programmable, it also contained a motorized magnetic card reader - and still fit into Bill Hewlett's shirt pocket. Experience this revolutionary calculator on your iPhone. With over 180 original HP programs included with the app, you can get started right away. "A work of art. Fantastic!" (MacBreak Weekly, episode 572) Features: • Virtual program and data cards • Virtual 2000-line paper tape printer supports AirPrint • Powerful database-driven card manager • Create, delete, label, and organize a virtually unlimited number of cards • Sharing: e-mail, AirDrop, Dropbox, iTunes, copy, paste, print • Paste existing HP-65 listings into RPN-65 and run them • "Live" display of stack, memory registers, program counter, flags • Reads program and data cards created by RPN-65 Pro • Reads data cards created by RPN-67 Pro/SD and RPN-97 Pro Run RPN-65 SD in any of 4 modes: 1 - Just like the original HP-65 2 - Like the original HP-65, but at much higher speed 3 - With many user-interface improvements, like backstep key or jump to any program step 4 - "Super-65" with 999 program steps, 120 labels, 120 registers, nested subroutines, and much more For details, free program downloads, calculator handbook and much more, visit the RPN-65 website: cuveesoft.ch/rpn65
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Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
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BUILD KIT DIFFICULTY
Advanced
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.
