App Overview

12Calc icon

12Calc

Ernest Brock · Finance

12Calc is a full version of the well known HP12C for the iPhone and iPad

$8.99 · In-app purchases

PRICE
$8.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
4.9
919 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.

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.

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

> SELECT BUILD PLATFORM:

Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.

// RORK SYSTEM PROMPT
Rork plan preview for 12Calc: map the core Finance 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

Implement a glossary feature with simplified explanations.

Assumption to check: Users report difficulty in understanding complex financial terms

Validate with people who use this workflow before building.

Hypothesis 2

Adopt a more minimalist design and enhance user experience.

Assumption to check: Some users find the UI cluttered and overwhelming

Validate with people who use this workflow before building.

Hypothesis 3

Integrate bank account linking for easier financial tracking.

Assumption to check: Inability to sync transactions with bank accounts automatically

Validate with people who use this workflow before building.

Hypothesis 4

Enable users to create and modify categories as per their needs.

Assumption to check: Limited customization options for categories and transactions

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

12Calc is a full version of the well known HP12C for the iPhone and iPad. It also includes an audit tape, unit converter, worksheets, rotated views, user guide and HD graphics optimized for iPad and iPhone retina displays. •Runs in 64 bit mode on the latest iOS release and new iPads and iPhones. •Calculations are highly accurate and blazing fast. No more "running" flashing displays for amortizations, depreciation schedules or interest calculations. Work as fast as you can type. •Audit Tape: The audit tape keeps a record of your calculations. You can review, mail, text, share or print the tape. •Unit Converter: Convert between a wide variety of common units and currencies. Currency rates can be downloaded from the internet. •Work Sheets with interactive graphs: Auto Purchase Black-Scholes Bond Break-even Cash Flow analysis Currency Date Depreciation Interest Conversion Lease Loan Amortization (includes option for Canadian mortgages) Margin&Markup Refinance Statistics Tip TVM •Views for all orientations: Portrait and landscape renderings of the full keyboard are provided for iPhone and iPad. The iPad version includes slide over and multiple split view displays as well as side-by-side display of the help page, audit tape, tvm mortgage table or program variables. •Built-in contextual help: Touch the ? key for a description of any keyboard function with examples of use. If you are just learning or can't remember how to use a function- just touch the ? key. Includes tutorials on how to use reverse Polish notation (RPN) and how to solve time value of money problems. •HD Graphics: Graphics optimized for both retina and standard resolution screens. Choose from multiple color schemes including gold, rose gold, brass, copper, silver and several color tints.

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
Zustand
@react-navigation/native
react-native-gesture-handler
axios
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.