3. When preparing the report referred to in paragraph 1, first subparagraph, of this Article, operators shall make use of the best available information. Operators shall obtain the data by means of measurement. Where measurement does not result in the best available information, is not practicable or is not technologically and economically viable, operators shall obtain the data by means of calculation. Where neither measurement nor calculation is practicable, operators may obtain the data by estimation. The information may include monitoring data, emission factors, mass balance equations, indirect monitoring or other calculations, engineering judgements and other methods that are in accordance with Article 9(1) and, where available, internationally approved methodologies.