The chapter number. Every chapter should be assigned a chapter number.

The depth of numbering for section. All sections are numbered relative to their surrounding chapter/sections. The fourth section of of the first section of chapter three would be section 3.1.4, if displayed at the default number depth of three. To omit the chapter number, a number depth of 2 should be used. In that case, the section number would be displayed as 1.4.