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
Nautical Calculator Pro
Nautical Calculator Pro is the most complete application that solves the navigation calculations
$8.99 · In-app purchases
PRICE
$8.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
3 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 included18 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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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Nautical Calculator Pro: map the core Navigation 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
Add advanced features like tide calculations and weather integration
Assumption to check: Limited functionality for complex navigation calculations
Validate with people who use this workflow before building.
Hypothesis 2
Offer a freemium model with essential features for free
Assumption to check: High price point for a niche audience
Validate with people who use this workflow before building.
Hypothesis 3
Implement a user forum or sharing options for calculations
Assumption to check: Lack of community support or user sharing features
Validate with people who use this workflow before building.
Hypothesis 4
Simplify the UI and add tutorials for beginners
Assumption to check: Complexity of use for non-sailors
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
Nautical Calculator Pro is the most complete application that solves the navigation calculations The main features are : - Calculate Route (solves 2nd navigation problem) - Calculate point on Rhumb Line (solves 1st navigation problem) - Calculate point on Great Circle (solves 1st navigation problem) - Calculate point on WGS84 (solves 1st navigation problem) - Calculate Average speed - E.T.A. calculation - Route plan, for manual waypoints planning - Waypoint route - Compisite sailing with parallel limit - Rhumb Line Parallel/Meridian intersection - Follow on same Rhumb Line route - Opposite course rendez vous - Route correction - Calculate Amplitude at sunset and sunrise and magnetic compass deviation - Compass detections - Solves Drift problem - Solves Tides problem - Solves Tidal current problem - Wind calculation with Beaufort classification - ABC Tables (azimuth, initial course, right ascension with unknow star) - Nautical almanac - Celestial Navigation with position line - Meridian transit - Celestial observation - Coastal navigation - Wheel Over - Draft survey - Converter - Anchorage - Interpolation In routes feature there is a world map: it isn't a nautical chart and is not for use as a saling chart, but as a simple general means of showing the courses through the water on earth, this map isn't for navigational purposes. No need connection for show the map; the map will be downloaded only one time. The map, for size limit, will be show for scale over 60-70 Nm. follow on facebook https://www.facebook.com/NauticalCalculator
Written user reviews are not shown here. Check current App Store reviews >
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.
SUGGESTED BUILD STACK
React Navigation
Expo
react-native-paper
expo-linear-gradient
React Native
BUILD KIT DIFFICULTY
Intermediate
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.
