The final letter makes up the "subclass" (subclass A01B represents "Soil working in agriculture or forestry; parts, details, or accessories of agricultural machines or implements, in general"). The subclass is followed by a one-to-three-digit "group" number, an oblique stroke and a number of at least two digits representing a "main group" or "subgroup". A patent examiner assigns classification symbols to patent application or other document in accordance with classification rules, and generally at the most detailed level which is applicable to its content.