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
Nautical Calculator is an easy to use app to help solve the equations and conversions typically associated with marine navigation and includes celestial calculators, conversions calculators, distance calculators, loga...
$8.99 · In-app purchases
PRICE
$8.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
4 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 included15 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: 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
Offer a wider range of calculators and tools.
Assumption to check: Limited calculators available compared to competitors.
Validate with people who use this workflow before building.
Hypothesis 2
Implement offline capabilities for calculations.
Assumption to check: No offline functionality.
Validate with people who use this workflow before building.
Hypothesis 3
Introduce a subscription model with a free trial.
Assumption to check: High one-time purchase price.
Validate with people who use this workflow before building.
Hypothesis 4
Provide in-app tutorials or guides for new users.
Assumption to check: Lack of user tutorials or help sections.
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 is an easy to use app to help solve the equations and conversions typically associated with marine navigation and includes celestial calculators, conversions calculators, distance calculators, logarithm and trigonometry calculators, and sailings calculators. This app is the finest nautical calculator you will find for the Apple iPhone, iPad, and iPod Touch and includes the computations, tables, and full text of the "The American Practical Navigator" by Nathaniel Bowditch. With more than 35 nautical calculations, unit conversions and reference material, we are sure you will find this app convenient in solving the planning and navigating problems associated with marine navigation. Calculations Include: Celestial Navigation Calculators ------------------------------------------------ 1. Compass Error from Amplitudes Observed on the Visible Horizon 2. Altitude Correction for Air Temperature 3. Table of Offsets 4. Latitude and Longitude Factors 5. Altitude Correction for Atmospheric Pressure 6. Altitude Factors & Change of Altitude 7. Pub 229 8. Compass Error from Amplitudes Observed on the Celestial Horizon 9. Meridian Angle and Altitude of a Body on the Prime Vertical Circle Conversions Calculators ------------------------------------------------ 1. Chart Scales and Conversion for Nautical and Statute Miles 2. Conversion for Meters, Feet and Fathoms Distance Calculators ------------------------------------------------ 1. Length of a Degree of Latitude and Longitude 2. Speed for Measured Mile and Speed, Time, and Distance 3. Distance of an Object by Two Bearings 4. Distance of the Horizon 5. Distance by Vertical Angle Measured Between Sea Horizon and Top of Object Beyond Sea Horizon 6. Traverse Table 7. Geographic Range 8. Distance by Vertical Angle Measured Between Waterline at Object and Top of Object 9. Dip of Sea Short of the Horizon 10. Distance by Vertical Angle Measured Between Waterline at Object and Sea Horizon Beyond Object 11. Meridional Parts Log and Trig Calculators ------------------------------------------------ 1. Log10 2. tangent 3. cosecant 4. sine 5. cotangent 6. cosine 7. secant Sailings Calculators ------------------------------------------------ 1. Great Circle Sailing 2. Mercator Sailing Time Zones Calculators ------------------------------------------------ 1. Time Zones 2. Zone Descriptions, and Suffixes Weather Data Calculators ------------------------------------------------ 1. Direction and Speed of True Wind 2. Correction of Barometer Reading for Height Above Sea Level 3. Correction of Barometer Reading for Gravity 4. Temperature Conversions 5. Relative Humidity and Dew Point 6. Correction of Barometer Reading for Temperature 7. Barometer Measurement Conversions Included Reference Documents ------------------------------------------------ 1. AMERICAN PRACTICAL NAVIGATOR - VOL 1 2. AMERICAN PRACTICAL NAVIGATOR - VOL 2 3. SIGHT REDUCTION TABLES VOL 1 0° - 15° 4. SIGHT REDUCTION TABLES VOL 2 15° - 30° 5. SIGHT REDUCTION TABLES VOL 3 30° - 45° 6. SIGHT REDUCTION TABLES VOL 4 45°- 60° 7. SIGHT REDUCTION TABLES VOL 5 60°- 75° 8. SIGHT REDUCTION TABLES VOL 6 75°- 90° Learn more at http://www.NauticalCalculator.com
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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.
SUGGESTED BUILD STACK
React Navigation
Zustand
Expo
React Native Paper
TypeScript
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.
