def convert(quantity)
      if Quantity===quantity
        assert_same_dimension(quantity.unit)
        v = quantity.unit.convert_value_to_base_unit(quantity.value)
        convert_value_from_base_unit(v)
      else
        quantity / to_numeric
      end
    end
def convert(quantity)
      if Quantity===quantity
        assert_same_dimension(quantity.unit)
        v = quantity.unit.convert_value_to_base_unit(quantity.value)
        convert_value_from_base_unit(v)
      else
        quantity / to_numeric
      end
    end
Convert a quantity to this unit.
 @param [Phys::Quantity] quantity to be converted.
 @return [Phys::Quantity]
 @raise [UnitError] if unit conversion is failed.