In his book “Dispareri in Materia d’Architettura, et Perspettiva” Martino Bassi distinguishes between two types of fonts. For the introduction he uses an artistic handwriting while he uses an easier to read, standardized font in the main part.
As far as I understand, the book displays an exchange of letters between Bassi and various architects in which Bassi starts every conversation with a new architect with changing the font size.
In that case the recipient is named in a title in large letters and the sender occurs as a subtitle in smaller letters. The correspondence between the two people follows. The first letter of each chapter is artfully decorated and much larger than the rest. In addition, all the texts are centred on each page, which means that at the end of a section, the letters converge in a V-shape. All the pages where something is written on on the left are numbered on the top left, whereas the pages on the right are numbered on the top right.
In my opinion, the illustrations are of less importance than the text, because they have been moved to the end of the book and their arrangement seems to be much less thought out than the arrangement of the text. They might have served for a better understanding when reading the letters or were possibly sent back and forth with the letters. While some of them are elaborated, detailed perspectives, others look more like quick sketches. After every image there is one page that is left empty. Furthermore, they are all numbered and each illustration has a short description at the bottom.
The book seems to be a mixture between an academic study and a diary-like process to find a consensus in dealing with the milanese cathedral. Which means it is kind of a specific history book.