enum Unit: int

• Inches = 1
• Millimetres = 2
• Custom = 3
• Feet = 4
• Miles = 5
• Meters = 6
• Kilometers = 7
• Mils = 8
• Microns = 9
• Centimeters = 10
• Microinches = 11

operator>>(std::istream & in, Unit & rhs) -> std::istream &

operator<<(std::ostream & out, Unit rhs) -> std::ostream &

to_string(Unit rhs) -> const char *

unit_name(Unit unit) -> string