Except where a rate of yield has been specified in Community legislation governing specific fields, the customs authorities shall set either the rate of yield or average rate of yield of the processing operation or where appropriate, the method of determining such rate.
The rate of yield or average rate of yield shall be determined on the basis of the actual circumstances in which processing operations are, or are to be, carried out. That rate may be adjusted, where appropriate, in accordance with Articles 18 and 19.