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
Heart Rate Variability Logger
Heart Rate Variability Logger lets you record, plot and export time, frequency and non-linear HRV Features (includes experience sampling, RR-interval correction, DFA alpha 1 for aerobic threshold estimation in real-ti...
$9.99 · In-app purchases
PRICE
$9.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.6
18 ratings · Top 50%
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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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 Heart Rate Variability Logger: map the core Health & Fitness 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
Integrate AI insights based on logged data.
Assumption to check: Limited analysis features for advanced users.
Validate with people who use this workflow before building.
Hypothesis 2
Standardize input fields and use dropdowns for common values.
Assumption to check: Inconsistent data entry methods.
Validate with people who use this workflow before building.
Hypothesis 3
Add customizable notification settings for reminders.
Assumption to check: Poor user engagement due to lack of reminders.
Validate with people who use this workflow before building.
Hypothesis 4
Redesign with contemporary UI/UX principles for better user experience.
Assumption to check: UI could be more modern.
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
Heart Rate Variability Logger lets you record, plot and export time, frequency and non-linear HRV Features (includes experience sampling, RR-interval correction, DFA alpha 1 for aerobic threshold estimation in real-time, comparison between recordings, activity monitoring & step counting, location tracking). Heart Rate Variability Logger requires a Bluetooth Low Energy (also called Bluetooth Smart or BLE or 4.0) heart rate sensor (we recommend Polar H7 or H10) Main features: - Extracts, plots, stores and exports heart rate, rr-intervals, time and frequency domain heart rate variability features (AVNN, SDNN, rMSSD, pNN50, LF, HF, LF/HF, alpha 1 from DFA) - Configurable experience sampling for events annotation - Comparison between up to 3 recordings lets you get a better understanding of differences in HRV under different contexts in a glance. The comparison modality includes also Outlier removal - Activity tracking: step counter or accelerometer derived motion intensity for user context (step counter only for iPhones 5S) - Location tracking, either using GSM/WiFi networks (low battery consumption) or GPS (high accuracy) - Configurable time window for features computation (choose between 30 seconds, 1, 2 or 5 minutes) - RR-intervals correction can be enabled to prevent ectopic beats or artifacts from affecting HRV features - export for Kubios - Filters data based on the selected threshold - Shows HR in the app icon - Data export using iTunes or Dropbox - Tested for recordings longer than 24 hours Please note that continued use of GPS running in the background can dramatically decrease battery life.
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.
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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.
