Operation between quantities having different units, like km and mile , with automatic unit conversion. Refer to Notation of unit below.
Operation is made after the unit of other is converted to the unit of self .
Exception is raised if unit conversion is failed. Return the Quanty class instance with the unit of self . Resulting unit is made by concatenating self and other . If self is a quantity with a dimensionless unit, return its value. If self is a quantity with an angular unit, return the value converted into radian.