code: def measurement_set(type, value, unit)
        measure = measurement(type)
  
        # create a new isbn record if we need to
        if measure.nil?
          measure = ONIX::Measure.new
          measure.measure_type_code = type
          product.measurements << measure
        end
  
        # store the new value
        measure.measurement = value
        measure.measure_unit_code = unit.to_s
      end
docs: set the value of a particular measurement