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
Psychrometric Chart
Interactive, graphical psychrometric chart app for HVAC engineers and designers
$59.99 · In-app purchases
PRICE
$59.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.4
34 ratings · Top 30%
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 included14 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
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 Psychrometric Chart: 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 interactive tutorials and simplified views for beginners.
Assumption to check: Users often find psychrometric charts complex and hard to interpret.
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to customize colors and styles of the chart.
Assumption to check: Limited customization options for chart display.
Validate with people who use this workflow before building.
Hypothesis 3
Optimize chart rendering for faster performance.
Assumption to check: Some users report performance issues with large data sets.
Validate with people who use this workflow before building.
Hypothesis 4
Offer tiered pricing or a freemium model to attract more users.
Assumption to check: In-app purchase prices are considered high by some 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
Interactive, graphical psychrometric chart app for HVAC engineers and designers. Allows you to create and manipulate charts and state points with the touch of your finger(s). Processes that can be modeled include: • An individual state point. • Air mixing. • Sensible heating. • Sensible cooling. • Cooling coils. • Other processes by connecting state points. Add new state points by double tapping anywhere on the chart. Hold and drag existing state points to move them on the graph, with properties values updating live to aid you in setting them to the right value. Works in both SI and IP units. Allows you to create and save multiple charts. Properties and energy change for connected points are calculated and displayed live. Share your charts by exporting a PDF file or sending to an AirPrint device. Works on both the iPhone and iPad, but best used on the larger screen of the iPad. ------ We would very much like your feedback! Suggestions, complements, complaints, bug reports etc.: http://www.pheinex.com/contact/ If you like this app, please do not forget to rate it in the App Store! ----- Notes: This application (App) is provided for use by qualified HVAC engineers and designers in the design of air handling systems and is not a substitute for appropriate design services. When in doubt, contact a design
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 Native
Expo
react-navigation
axios
zustand
react-native-reanimated
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.
