Metric System:
- Millimeter (mm): 1/1000 meter
- Centimeter (cm): 1/100 meter  
- Meter (m): Base unit
- Kilometer (km): 1000 meters

Imperial System:
- Inch (in): Base small unit
- Foot (ft): 12 inches
- Yard (yd): 3 feet = 36 inches
- Mile (mi): 5,280 feet = 1,760 yards

1 meter = 3.28084 feet
1 inch = 2.54 centimeters
1 mile = 1.60934 kilometers
1 yard = 0.9144 meters
1 kilometer = 0.621371 miles
1 foot = 30.48 centimeters

Maritime & Aviation:
- Nautical Mile: 1,852 meters
- Fathom: 6 feet (depth measurement)
- Cable: 1/10 nautical mile

Scientific:
- Angstrom (Å): 10^-10 meters (atomic scale)
- Light-year: 9.461 × 10^15 meters
- Parsec: 3.086 × 10^16 meters
- Astronomical Unit (AU): 149.6 million km

Historical:
- Cubit: ~18-22 inches (ancient measurement)
- Rod/Pole: 16.5 feet
- Furlong: 660 feet = 1/8 mile
- League: ~3 miles (varies by region)

Mass: Amount of matter (constant everywhere)
Weight: Force due to gravity (varies by location)

On Earth: 1 kg mass = 9.8 Newtons weight
On Moon: 1 kg mass = 1.6 Newtons weight

Metric System:
- Milligram (mg): 1/1000 gram
- Gram (g): Base small unit
- Kilogram (kg): 1000 grams
- Metric Ton (t): 1000 kilograms

Imperial/US System:
- Ounce (oz): Base small unit
- Pound (lb): 16 ounces
- Stone (st): 14 pounds (UK)
- US Ton: 2000 pounds
- UK Ton (Long Ton): 2240 pounds

1 kilogram = 2.20462 pounds
1 pound = 16 ounces = 453.592 grams
1 ounce = 28.3495 grams
1 stone = 14 pounds = 6.35029 kilograms
1 metric ton = 1000 kg = 2204.62 pounds

Precious Metals:
- Troy Ounce: 31.1035 grams (gold, silver)
- Pennyweight: 1/20 troy ounce
- Grain: 1/7000 pound = 64.79891 mg

Scientific:
- Atomic Mass Unit (u): 1.66054 × 10^-27 kg
- Carat: 200 mg (gemstones)
- Dalton: Same as atomic mass unit

Medical/Pharmaceutical:
- Milligram (mg): Medicine dosages
- Microgram (μg): Vitamin dosages
- Parts per Million (ppm): Concentration

Celsius (°C):
- Water freezes: 0°C
- Water boils: 100°C
- Absolute zero: -273.15°C

Fahrenheit (°F):
- Water freezes: 32°F
- Water boils: 212°F
- Absolute zero: -459.67°F

Kelvin (K):
- Absolute temperature scale
- Water freezes: 273.15 K
- Water boils: 373.15 K
- Absolute zero: 0 K

Rankine (°R):
- Fahrenheit-based absolute scale
- Water freezes: 491.67°R
- Water boils: 671.67°R
- Absolute zero: 0°R

// Celsius to Fahrenheit
°F = (°C × 9/5) + 32

// Fahrenheit to Celsius  
°C = (°F - 32) × 5/9

// Celsius to Kelvin
K = °C + 273.15

// Fahrenheit to Rankine
°R = °F + 459.67

// Kelvin to Rankine
°R = K × 9/5

Common Temperatures:
- Room Temperature: 20-25°C (68-77°F)
- Human Body: 37°C (98.6°F)
- Comfortable Bath: 40°C (104°F)
- Hot Coffee: 60-70°C (140-158°F)
- Oven Baking: 180°C (356°F)

Extreme Temperatures:
- Liquid Nitrogen: -196°C (-321°F)
- Dry Ice: -78.5°C (-109.3°F)
- Death Valley Record: 54.4°C (129.9°F)
- Furnace Steel: 1500°C (2732°F)
- Sun's Surface: 5778 K (5505°C, 9941°F)

Metric Area Units:
- Square Millimeter (mm²)
- Square Centimeter (cm²): 100 mm²
- Square Meter (m²): 10,000 cm²
- Hectare (ha): 10,000 m²
- Square Kilometer (km²): 100 ha

Imperial Area Units:
- Square Inch (in²): Base unit
- Square Foot (ft²): 144 in²
- Square Yard (yd²): 9 ft²
- Acre: 4,840 yd² = 43,560 ft²
- Square Mile (mi²): 640 acres

Metric Volume Units:
- Milliliter (mL): 1/1000 liter
- Liter (L): Base unit
- Cubic Centimeter (cm³): = 1 mL
- Cubic Meter (m³): 1000 liters

Imperial Volume Units:
- Fluid Ounce (fl oz): Base liquid unit
- Cup: 8 fl oz
- Pint: 2 cups = 16 fl oz
- Quart: 2 pints = 32 fl oz
- Gallon: 4 quarts = 128 fl oz

Dry Volume:
- Cubic Inch (in³)
- Cubic Foot (ft³): 1,728 in³
- Cubic Yard (yd³): 27 ft³

Area Conversions:
1 square meter = 10.7639 square feet
1 acre = 4,047 square meters
1 hectare = 2.47105 acres
1 square mile = 2.59 square kilometers

Volume Conversions:
1 liter = 0.264172 US gallons
1 US gallon = 3.78541 liters
1 cubic meter = 264.172 US gallons
1 imperial gallon = 4.54609 liters

Common Speed Units:
- Meters per Second (m/s): SI base unit
- Kilometers per Hour (km/h): Metric standard
- Miles per Hour (mph): Imperial standard
- Knots: Nautical/aviation (1 kt = 1 nm/h)
- Feet per Second (ft/s): Engineering

Specialized Speed Units:
- Mach: Speed of sound multiples
- c: Speed of light (299,792,458 m/s)
- Furlongs per Fortnight: Humorous unit

Speed Equivalents:
1 m/s = 3.6 km/h = 2.237 mph = 3.281 ft/s
1 km/h = 0.278 m/s = 0.621 mph = 0.540 knots
1 mph = 0.447 m/s = 1.609 km/h = 0.868 knots
1 knot = 0.514 m/s = 1.852 km/h = 1.151 mph

Reference Speeds:
- Walking: 5 km/h (3.1 mph)
- Cycling: 20 km/h (12.4 mph)
- City Driving: 50 km/h (31 mph)
- Highway: 100 km/h (62 mph)
- Commercial Jet: 900 km/h (560 mph, Mach 0.85)
- Sound at Sea Level: 343 m/s (Mach 1)

Common Acceleration Units:
- m/s² (meters per second squared): SI unit
- ft/s² (feet per second squared): Imperial
- g (standard gravity): 9.80665 m/s²

Examples:
- Earth Gravity: 1 g = 9.81 m/s²
- Car Acceleration: 0-60 mph in 6s ≈ 0.46 g
- Space Shuttle Launch: ~3 g
- Formula 1 Braking: ~5 g
- Jet Fighter: Up to 9 g

Scientific Energy Units:
- Joule (J): SI base unit (1 N⋅m)
- Kilojoule (kJ): 1000 J
- Calorie (cal): 4.184 J (thermochemical)
- Kilocalorie (kcal): 1000 cal (food calories)
- British Thermal Unit (BTU): 1055.06 J

Electrical Energy:
- Kilowatt-hour (kWh): 3.6 MJ
- Electronvolt (eV): 1.602 × 10^-19 J
- Therm: 100,000 BTU = 105.5 MJ

Large Scale Energy:
- Ton of TNT: 4.184 GJ
- Ton of Oil Equivalent (toe): 41.868 GJ
- Quad: 10^15 BTU

Power Units:
- Watt (W): SI base unit (1 J/s)
- Kilowatt (kW): 1000 W
- Horsepower (hp): 745.7 W
- Metric Horsepower (PS): 735.5 W
- BTU per Hour: 0.293 W

Power Examples:
- LED Bulb: 10 W
- Microwave: 1000 W = 1 kW
- Hair Dryer: 1500 W
- Electric Car: 200-400 kW
- Wind Turbine: 1-3 MW
- Power Plant: 500-2000 MW

Food Energy:
1 food Calorie = 1 kcal = 4184 J
Big Mac: ~550 kcal = 2.3 MJ

Household Energy:
Average Home: 30 kWh/day = 108 MJ/day
Electric Car (Tesla): 75 kWh battery = 270 MJ

Combustion Energy:
1 gallon gasoline: 33.7 kWh = 121 MJ
1 kg wood: ~15 MJ
1 kg coal: ~30 MJ
1 kg uranium (fission): ~80 TJ

Basic Time Units:
- Second (s): SI base unit
- Minute (min): 60 s
- Hour (h): 60 min = 3600 s
- Day: 24 h = 86,400 s
- Week: 7 days
- Month: ~30.44 days (average)
- Year: 365.25 days (accounting for leap years)

Precise Time Units:
- Millisecond (ms): 1/1000 s
- Microsecond (μs): 1/1,000,000 s  
- Nanosecond (ns): 1/1,000,000,000 s
- Picosecond (ps): 1/1,000,000,000,000 s

Large Time Units:
- Decade: 10 years
- Century: 100 years
- Millennium: 1000 years

Frequency Units:
- Hertz (Hz): 1 cycle per second
- Kilohertz (kHz): 1000 Hz
- Megahertz (MHz): 1,000,000 Hz
- Gigahertz (GHz): 1,000,000,000 Hz

Common Frequencies:
- AC Power: 50-60 Hz
- AM Radio: 530-1700 kHz
- FM Radio: 88-108 MHz
- WiFi: 2.4 GHz, 5 GHz
- CPU Clock: 2-5 GHz
- Visible Light: 430-750 THz

Relationship: Period = 1/Frequency

Examples:
- 60 Hz AC power → Period = 16.7 ms
- 1 MHz signal → Period = 1 μs
- 2.4 GHz WiFi → Period = 0.42 ns

Decimal (SI) Units:
- Kilobyte (KB): 1000 bytes
- Megabyte (MB): 1000 KB = 10^6 bytes
- Gigabyte (GB): 1000 MB = 10^9 bytes
- Terabyte (TB): 1000 GB = 10^12 bytes
- Petabyte (PB): 1000 TB = 10^15 bytes

Binary (IEC) Units:
- Kibibyte (KiB): 1024 bytes = 2^10 bytes
- Mebibyte (MiB): 1024 KiB = 2^20 bytes
- Gibibyte (GiB): 1024 MiB = 2^30 bytes
- Tebibyte (TiB): 1024 GiB = 2^40 bytes
- Pebibyte (PiB): 1024 TiB = 2^50 bytes

Common File Sizes:
- Text Document: 1-100 KB
- Digital Photo (JPEG): 1-10 MB
- Song (MP3): 3-5 MB
- HD Movie: 1-5 GB
- 4K Movie: 10-25 GB
- Video Game: 20-100 GB

Storage Devices:
- USB Flash Drive: 8 GB - 1 TB
- SSD Drive: 128 GB - 8 TB
- Hard Drive: 500 GB - 20 TB
- Blu-ray Disc: 25-100 GB

Connection Speeds:
- Dial-up: 56 Kbps
- DSL: 1-25 Mbps
- Cable Internet: 10-500 Mbps
- Fiber Internet: 100 Mbps - 1 Gbps
- WiFi 6: Up to 9.6 Gbps
- Ethernet: 10 Mbps - 400 Gbps
- USB 3.0: 5 Gbps
- Thunderbolt 3: 40 Gbps

Note: bps = bits per second, B/s = bytes per second
1 byte = 8 bits, so 1 Mbps = 0.125 MB/s

Real-time Exchange Rates:
- 150+ world currencies
- Live market data updates
- Historical rate tracking
- Cryptocurrency support

Major Currency Codes:
- USD: US Dollar
- EUR: Euro
- GBP: British Pound
- JPY: Japanese Yen
- CHF: Swiss Franc
- CAD: Canadian Dollar
- AUD: Australian Dollar
- CNY: Chinese Yuan

Interest Rate Conversions:
- Annual Percentage Rate (APR)
- Effective Annual Rate (EAR)
- Monthly/Daily rate calculations
- Compound interest formulas

Investment Units:
- Basis Points: 1 bp = 0.01%
- Percentage Points: 1 pp = 1%
- Return on Investment (ROI)
- Annual Growth Rate

Pressure Conversions:
- Pascal (Pa): SI base unit (N/m²)
- Kilopascal (kPa): 1000 Pa
- Megapascal (MPa): 1,000,000 Pa
- Bar: 100,000 Pa = 100 kPa
- Atmosphere (atm): 101,325 Pa
- PSI: Pounds per Square Inch
- mmHg: Millimeters of Mercury
- Torr: 1/760 atm ≈ 133.32 Pa

Reference Pressures:
- Sea Level: 1 atm = 14.7 PSI = 101.325 kPa
- Car Tire: 30-35 PSI = 207-241 kPa
- Scuba Tank: 3000 PSI = 20.7 MPa
- Deep Ocean (10 km): 1100 atm

Basic Electrical Units:
- Volt (V): Electric potential
- Ampere (A): Electric current  
- Ohm (Ω): Electrical resistance
- Watt (W): Electrical power
- Farad (F): Capacitance
- Henry (H): Inductance

Power Relationships:
P = V × I (Power = Voltage × Current)
V = I × R (Ohm's Law)
P = V²/R = I²R (Power calculations)

Common Values:
- AA Battery: 1.5 V
- Car Battery: 12 V
- Household Outlet: 120 V (US), 240 V (EU)
- Power Line: 11-765 kV

Radiation Measurements:
- Becquerel (Bq): Activity (decays/second)
- Curie (Ci): 37 billion Bq
- Gray (Gy): Absorbed dose (J/kg)
- Rad: 0.01 Gy
- Sievert (Sv): Equivalent dose
- Rem: 0.01 Sv

Typical Exposure Levels:
- Chest X-ray: 0.1 mSv
- Annual Background: 2-3 mSv
- CT Scan: 7 mSv
- Flight (NY-LA): 0.04 mSv
- Banana (potassium): 0.0001 mSv

Significant Figures:
- Input: Maintains original precision
- Calculation: IEEE 754 double precision
- Output: Configurable decimal places
- Scientific Notation: For very large/small numbers

Error Handling:
- Invalid input detection
- Overflow/underflow protection
- Precision loss warnings
- Unit compatibility checking

Multi-Value Processing:
- CSV file import/export
- Range calculations
- Statistical analysis
- Unit validation

Formula Integration:
- Custom conversion factors
- Compound unit calculations
- Multi-step conversions
- Engineering calculations

// Example API usage
const converter = new UnitConverter();

// Basic conversion
const result = converter.convert(100, 'celsius', 'fahrenheit');
console.log(result); // 212

// Batch conversion
const values = [0, 100, 200];
const results = converter.convertBatch(values, 'kg', 'lb');
console.log(results); // [0, 220.46, 440.92]

// Precision control
const precise = converter.convert(1/3, 'm', 'ft', {precision: 10});
console.log(precise); // 1.0936132983

Measurement Precision Guidelines:
- Use appropriate significant figures
- Consider measurement uncertainty
- Round final results appropriately
- Document precision requirements

System Selection:
- Scientific: Use SI (metric) units
- Engineering: Consider industry standards
- International: Use metric for global compatibility
- Legacy: Convert historical measurements

Accuracy Checks:
- Cross-reference with known values
- Use multiple conversion methods
- Verify unit compatibility
- Check for reasonable results

Avoid These Errors:
- Confusing mass and weight
- Wrong temperature formulas
- Decimal vs binary storage units
- Mixing unit systems mid-calculation
- Ignoring significant figures