diff --git a/PRD.md b/PRD.md
index 82a9896..dc4a928 100644
--- a/PRD.md
+++ b/PRD.md
@@ -15,6 +15,13 @@ TheNoiseClock is a SwiftUI-based iOS application that combines a customizable di
 - **Portrait and landscape orientation support** with responsive font sizing
 - **Optimal font sizing** that uses all available space efficiently
 - **Immediate updates** on orientation changes and tab bar visibility changes
+- **Fixed-width digit rendering** to prevent layout shifts and jumping
+- **Individual digit views** with consistent spacing and alignment
+- **Font customization** with family, weight, and design selection
+- **Dynamic dot sizing** that matches selected font weight
+- **Safe area handling** with proper Dynamic Island avoidance
+- **Full-screen mode** with status bar hiding and tab bar expansion
+- **Orientation-aware spacing** for optimal layout in all orientations
 
 ### 2. Clock Customization
 - **Color customization**: User-selectable digit colors with color picker
@@ -24,12 +31,21 @@ TheNoiseClock is a SwiftUI-based iOS application that combines a customizable di
 - **Opacity controls**: Separate opacity for clock digits and overlays
 - **Random color mode**: Automatically changes digit color every minute
 - **Preset themes**: Quick "Night" (black/white) and "Day" (white/black) themes
+- **Font family selection**: Choose from System, San Francisco, Monaco, Courier fonts
+- **Font weight options**: Ultra Light, Thin, Light, Regular, Medium, Semibold, Bold, Heavy, Black
+- **Font design choices**: Default, Serif, Rounded, Monospaced designs
+- **Live font preview**: Real-time preview of font changes in settings
+- **Font persistence**: All font settings saved and restored automatically
 
 ### 3. Display Modes
 - **Normal mode**: Standard interface with navigation and settings
 - **Display mode**: Full-screen clock activated by long-press (0.6 seconds)
 - **Automatic UI hiding**: Tab bar and navigation elements hide in display mode
 - **Smooth transitions**: Animated transitions between modes
+- **Status bar control**: Status bar automatically hidden in full-screen mode
+- **Safe area expansion**: Clock expands into tab bar area when hidden
+- **Dynamic Island awareness**: Proper spacing to avoid Dynamic Island overlap
+- **Orientation handling**: Full-screen mode works in both portrait and landscape
 
 ### 4. Information Overlays
 - **Battery level display**: Real-time battery percentage with icon
@@ -70,6 +86,44 @@ TheNoiseClock is a SwiftUI-based iOS application that combines a customizable di
 - **Next trigger preview**: Shows when the next alarm will fire
 - **Responsive time picker**: Font sizes adapt to available space and orientation
 
+## Advanced Clock Display Features
+
+### Fixed-Width Digit Rendering
+- **Individual digit views**: Each digit (0-9) rendered in its own view component
+- **Consistent spacing**: All digits use the width of the widest digit ("8") for uniform layout
+- **Height consistency**: All digits use the height of the tallest digit ("8") to prevent vertical jumping
+- **Layout stability**: No shifting or jumping when time changes (e.g., "11" to "12")
+- **Perfect centering**: Each digit is centered within its fixed-width container
+
+### Font Customization System
+- **Font family selection**: System, San Francisco, Monaco, Courier options
+- **Weight variations**: 9 weight options from Ultra Light to Black
+- **Design choices**: Default, Serif, Rounded, Monospaced designs
+- **Live preview**: Real-time font preview in settings interface
+- **UIFont integration**: Proper font measurement for accurate sizing
+- **Weight-based dot scaling**: Colon dots automatically scale with font weight
+
+### Dynamic Layout and Sizing
+- **GeometryReader integration**: Real-time container size detection
+- **Orientation-aware calculations**: Different sizing algorithms for portrait vs landscape
+- **Safe area handling**: Proper Dynamic Island avoidance and tab bar expansion
+- **Maximum space utilization**: Font sizes calculated to use all available space
+- **Responsive updates**: Immediate recalculation on orientation or layout changes
+
+### Advanced Spacing and Alignment
+- **Orientation-aware spacing**: Different spacing values for portrait vs landscape
+- **Consistent segment spacing**: Uniform spacing between hours, minutes, seconds
+- **Dot weight matching**: Colon dots scale with selected font weight
+- **Overflow prevention**: Spacing calculations prevent content clipping
+- **Perfect centering**: All elements centered both horizontally and vertically
+
+### Full-Screen Mode Enhancements
+- **Status bar hiding**: Automatic status bar hiding in full-screen mode
+- **Tab bar expansion**: Clock expands into tab bar area when hidden
+- **Safe area management**: Proper handling of Dynamic Island and other safe areas
+- **Smooth transitions**: Animated transitions between normal and full-screen modes
+- **Orientation support**: Full-screen mode works seamlessly in all orientations
+
 ## Technical Architecture
 
 ### Code Organization Principles
@@ -122,7 +176,9 @@ These principles are fundamental to the project's long-term success and must be
   - Visual settings (colors, glow, scale, opacity)
   - Overlay settings (battery, date, opacity)
   - Background settings
+  - Font customization (family, weight, design)
   - Color caching for performance optimization
+  - Persistent storage with JSON encoding/decoding
 - **Alarm**: Codable struct for comprehensive alarm data
   - UUID identifier
   - Time and enabled state
@@ -200,7 +256,7 @@ TheNoiseClock/
 │   │   └── View+Extensions.swift   # Common view modifiers and responsive utilities
 │   └── Utilities/
 │       ├── ColorUtils.swift        # Color manipulation utilities
-│       ├── FontUtils.swift         # Font sizing and typography utilities
+│       ├── FontUtils.swift         # Font sizing, typography, and customization utilities
 │       └── NotificationUtils.swift # Notification helper functions
 ├── Models/
 │   ├── ClockStyle.swift            # Clock customization data model
@@ -216,7 +272,7 @@ TheNoiseClock/
 │   │   ├── ClockView.swift         # Main clock display view
 │   │   ├── ClockSettingsView.swift # Clock customization interface
 │   │   └── Components/
-│   │       ├── TimeDisplayView.swift    # Segmented time display component
+│   │       ├── TimeDisplayView.swift    # Advanced segmented time display with fixed-width digits
 │   │       ├── BatteryOverlayView.swift # Battery level overlay
 │   │       ├── DateOverlayView.swift    # Date display overlay
 │   │       └── TopOverlayView.swift     # Combined overlay container
@@ -360,6 +416,17 @@ The following changes **automatically require** PRD updates:
 - **Combine**: Timer publishers and reactive programming
 - **Observation**: Modern state management with @Observable
 - **Foundation**: Core system frameworks and utilities
+- **UIKit**: UIFont integration for precise text measurement and font customization
+
+### Font and Typography Utilities
+- **FontUtils.optimalFontSize()**: Calculates optimal font size for portrait orientation
+- **FontUtils.maximumStretchedFontSize()**: Calculates maximum font size for stretched mode
+- **FontUtils.customFont()**: Creates SwiftUI Font with custom family, weight, and design
+- **FontUtils.customUIFont()**: Creates UIFont for precise text measurement
+- **FontUtils.weightMultiplier()**: Calculates dot size multiplier based on font weight
+- **FontUtils.calculateMaxTextWidth()**: Measures text width for fixed-width calculations
+- **FontUtils.calculateMaxTextHeight()**: Measures text height for consistent digit sizing
+- **FontUtils.timePickerFontSize()**: Optimized font sizing for DatePicker components
 
 ### Performance Considerations
 - **Smart timer management**: Conditional timers based on settings
@@ -370,6 +437,9 @@ The following changes **automatically require** PRD updates:
 - **Dictionary lookups**: O(1) alarm access instead of linear search
 - **Smooth animations**: Hardware-accelerated transitions
 - **Preloaded audio**: Instant sound playback
+- **Font measurement caching**: Efficient text size calculations
+- **Fixed-width calculations**: Pre-calculated digit dimensions for consistent layout
+- **Orientation-aware sizing**: Optimized font sizing algorithms for different orientations
 
 ## Future Enhancement Opportunities
 - **Additional sound types**: More white noise variants