def as(quantity, unit)
      begin
        convert(quantity, unit)
      rescue MeasurementError => e
        raise MeasurementError.new("No conversion path from #{self} to #{unit} - #{e}")
      end
    end
def as(quantity, unit)
      begin
        convert(quantity, unit)
      rescue MeasurementError => e
        raise MeasurementError.new("No conversion path from #{self} to #{unit} - #{e}")
      end
    end
Returns the given quantity converted from this Unit into the given unit.