Constructs a family with empty base unit and family name
Constructs a family with the given base unit and family name
Adds a conversion rule to convertor
Converts from in unit to out unit
Converts a given value from in unit to out unit
Base unit for this family
Family name
Key is a unit, it's assumed that all rules have the same base unit
The ConversionFamily class is an internal class that provides a conversion by holding all of the conversion rules for a single family