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+<!-- 3075674a-d8ff-42c4-9ab2-45b044ce3b25 281033a6-8c0c-431d-94b1-812cae00e512 -->
+# Scientific Calculator Implementation Plan
+
+## Overview
+
+Extend the existing calculator architecture in `Models/` to add scientific computing capabilities, following the project's C# coding standards with `m_` prefix for private fields, `#region` blocks, and XML documentation.
+
+## Implementation Steps
+
+### 1. Create Scientific Calculator Interface
+
+**File**: `Models/IScientificCalculator.cs`
+
+- Extend `ICalculator` interface
+- Add methods for scientific operations:
+- Trigonometric: `Sin()`, `Cos()`, `Tan()`, `Asin()`, `Acos()`, `Atan()`
+- Logarithmic: `Log()`, `Log10()`, `Ln()`
+- Power/Root: `Power()`, `SquareRoot()`, `CubeRoot()`, `NthRoot()`
+- Other: `Factorial()`, `Absolute()`, `Modulus()`
+- Constants: Properties for `Pi`, `E`
+
+### 2. Implement Scientific Calculator
+
+**File**: `Models/ScientificCalculator.cs`
+
+- Inherit from `Calculator` class
+- Implement `IScientificCalculator` interface
+- Use proper `#region` blocks (Private Fields, Constructors, Public Methods, Private Methods)
+- Add angle mode support (Degrees/Radians) with private field `m_angleMode`
+- Implement all scientific operations using `System.Math`
+- Include proper error handling (negative factorial, domain errors for trig)
+- Record operations in history (inherited from base)
+- Add XML documentation for all public methods
+
+### 3. Create Console Application
+
+**File**: `Demo/ScientificCalculatorApp.cs`
+
+- Create console UI with menu system
+- Display available operations grouped by category (Basic, Trigonometric, Logarithmic, Power/Root, Other)
+- Input validation for numbers and operation selection
+- Support for angle mode toggle (Degrees/Radians)
+- Display memory and history features
+- Exit option
+- Use proper `#region` blocks and follow naming conventions
+
+### 4. Create Comprehensive Unit Tests
+
+**File**: `Tests/ScientificCalculatorTests.cs`
+
+- Follow test naming: `MethodName_StateUnderTest_ExpectedBehavior`
+- Use Arrange-Act-Assert pattern
+- Test categories:
+- **Basic Operations**: Verify inherited Add/Subtract/Multiply/Divide still work
+- **Trigonometric Tests**: Test Sin/Cos/Tan in both degrees and radians, edge cases (0, 90, 180, 360 degrees)
+- **Inverse Trigonometric Tests**: Test Asin/Acos/Atan with valid ranges
+- **Logarithmic Tests**: Test Log/Log10/Ln with positive numbers, verify domain errors for negative/zero
+- **Power/Root Tests**: Test Power, SquareRoot, CubeRoot, NthRoot with various inputs
+- **Factorial Tests**: Test positive integers, zero, verify error for negatives
+- **Angle Mode Tests**: Verify degree/radian conversions work correctly
+- **Memory Tests**: Verify memory operations inherited from base
+- **History Tests**: Verify scientific operations are recorded
+- **Error Handling Tests**: Test all exception scenarios
+
+### 5. Update Existing Files (if needed)
+
+- Add namespace references if required
+- No changes to existing `ICalculator` or `Calculator` to maintain backward compatibility
+
+## Key Design Decisions
+
+- **Inheritance**: `ScientificCalculator` extends `Calculator` to reuse memory and history functionality
+- **Interface Hierarchy**: `IScientificCalculator` extends `ICalculator` for polymorphism
+- **Angle Handling**: Default to Radians, provide mode toggle, convert internally when needed
+- **Constants**: Expose `Math.PI` and `Math.E` as properties for convenience
+- **Error Handling**: Use specific exceptions (`ArgumentException`, `ArgumentOutOfRangeException`) with clear messages
+
+## Files to Create
+
+1. `Models/IScientificCalculator.cs` - Interface definition
+2. `Models/ScientificCalculator.cs` - Implementation (~200-250 lines)
+3. `Demo/ScientificCalculatorApp.cs` - Console application
+4. `Tests/ScientificCalculatorTests.cs` - Comprehensive unit tests (~500-600 lines)
+
+### To-dos
+
+- [ ] Create IScientificCalculator interface extending ICalculator with scientific operation methods
+- [ ] Implement ScientificCalculator class with all scientific operations, angle mode support, and error handling
+- [ ] Build console application with menu system for scientific calculator operations
+- [ ] Create comprehensive unit tests covering all scientific operations, edge cases, and error handling
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