# Quickstart: Geek Calculator

## Running the Calculator
1. Open `index.html` in any modern web browser
2. The calculator will load with a dark terminal-themed UI
3. Begin typing calculations or use mouse/touch to operate

## Basic Operations
- **Addition**: `5 + 3 =` → displays `8`
- **Subtraction**: `10 - 4 =` → displays `6`
- **Multiplication**: `6 * 7 =` → displays `42`
- **Division**: `15 / 3 =` → displays `5`
- **Parentheses**: `(2 + 3) * 4 =` → displays `20`
- **Percentage**: `100 + 10% =` → displays `110`
- **Sign Toggle**: Enter number then press `±` or `+/-` button

## RPN Mode
1. Toggle RPN mode using the RPN button
2. Enter numbers followed by operators
3. Example: To calculate `4 + 6`: `4 ENTER 6 +`
4. Use `ENTER` to push numbers onto the RPN stack
5. Available operations: `+`, `-`, `*`, `/`

## Keyboard Controls
- **Numbers**: 0-9 keys
- **Operators**: `+`, `-`, `*`, `/` keys
- **Equals**: `=` or `Enter` key
- **Clear**: `Escape` or `C` key
- **All Clear**: `Shift + C` or `Double Escape`
- **Decimal Point**: `.` key
- **Backspace**: `Backspace` key
- **RPN Enter**: `Enter` key in RPN mode
- **Toggle RPN**: `R` key
- **Command Palette**: `@` key
- **History**: `↑` and `↓` arrow keys
- **Help/Shortcuts**: `?` key

## Command Palette
- Press `@` to open the command palette
- Type commands like "clear", "history", "theme", etc.
- Provides quick access to calculator functions

## History Feature
- Previous calculations appear in history panel
- Use `↑` and `↓` arrow keys to navigate
- Click on history items to re-run calculations
- Limited to 50 most recent entries

## Accessibility Features
- Full keyboard navigation
- ARIA labels on all controls
- High contrast mode
- Screen reader compatible
- Visible focus indicators

## Troubleshooting
- If you see "Error", check your expression syntax
- For division by zero, the result will show "Infinity"
- If calculator doesn't respond, try clearing with `Escape`
- For offline use, ensure service worker is enabled in your browser

## Testing
- Unit tests for core math operations: Run `tests/index.html` in browser
- Tests cover basic arithmetic, RPN operations, and error conditions