The encyclopaedia was once very small, the first edition in 1768 only had 3 books. Slowly it became bigger. The last edition, the 15th, started in 1974, has 29 books, plus two indexes. It includes an extra book called Propædia, to classify knowledge. The 29 books and made up of a Macropædia and a Micropædia. The Macropædia is a larger one, with more detailed articles that can be as long as 300 pages, made up of 17 books, while the Micropædia is the smaller one with many much shorter articles that are usually less than 750 words. The Micropædia is used for fast-checking, but for more detailed information, people have to use the Macropædia. Each book is very big, more than 1,000 pages per book. Every year, an update book was published. The last yearbook was for 2018, published in 2017.