Goods classification rules determine tariff headings, preferring specific descriptions and the material giving goods their essential character. Classification of goods for tariff purposes is governed by heading terms and Chapter/Section Notes; references to articles or materials include incomplete, mixed or assembled forms. When multiple headings apply, preference is given to the most specific heading, then to the material or component giving goods their essential character, and finally to the last applicable heading in numerical order. Supplementary notes define sub-classification hyphenation, duty-basis conventions, unit specifications and chapter-specific definitions, and Chapters 24 and 27 apply these rules to tobacco products and petroleum products respectively, with tariff items, units and duty bases listed accordingly.