Nielsen Bookscan divides the year into 13 4-week periods. In such a way that the period shown by the PublishNews Nielsen list of Spain always refers to the sales of the four weeks prior to the date of the list.

The PublishNews Nielsen list for Spain is based on data provided by the Bookscan tool offered by Nielsen. The data is developed every four weeks based on book sales in large chain bookstores, department stores, supermarkets and independent bookstores in which Nielsen counts the number of books sold.

See the list here: Publishnews