* Large organizational unit. Typically, a textbook is divided into units, each of which covers a major topic or theme.
* Provides an overview. Units provide students with an overview of the material that will be covered in the unit, and help them to see how the different chapters and sections fit together.
Chapters:
* Medium organizational unit. Each unit is further divided into chapters, which cover specific subtopics within the unit.
* In-depth coverage. Chapters provide students with in-depth coverage of the material, and help them to develop a deep understanding of the subject matter.
Sections:
* Small organizational unit. Each chapter is further divided into sections, which cover specific subtopics within the chapter.
* Detailed information. Sections provide students with detailed information about the material, and help them to master the concepts that are being taught.
By dividing textbooks into units, chapters, and sections, publishers are able to organize the material in a logical way, and make it easier for students to learn the subject matter.