AP1<h2>Ancient binding</h2> The binding is ancient, probably from the 15th century when the codex was assembled. We can clearly see the wood and leather parts with the different parts holding the pieces together.&nbsp;The small hole just below the glued title flyleaf probably is the remain of an ancient nails holding a clasp or leather thread.

AP2<h2>Parchment scars</h2> We see here the remains of a parchment accident in the middle of a text. This scar may have been treated with stitches which do not remain today. Parchment was expensive and it was not always possible, especially for students, to acquire good quality material.

AP3<h2>Ruling the page</h2> Here, on the left of the image we see a series of regularly spaced small holes in the parchment. These were used to define the lines on which the main text was copied. This is what we call the “ruling” of a page. Usually these holes are not visible in manuscript because this part of the page is cut out after the text is copied. In the case at hand it was not done probably to save writing surface of the precious parchment.

AP4<h2>One very precious piece of text!</h2> In this small piece of text, we see the association of two Parisian astronomers: John of Lignères and John of Saxony.

AP4.1<h2>One very precious piece of text!</h2> They are the authors for the two most copied texts in alfonsine astronomy in the 14th and 15th century.&nbsp;This text is what we call an explicit (closing words) of a text by the astronomer 1️⃣ “Magistri Johannes pychardii de lineriis” (i.e. John of Lignères, second line). The text was copied by the hand of 2️⃣ “Johannes de danecowe” (i.e. John of Saxony, end of fourth and beginning of fifth lines). Moreover we learn that John of Lignères text was composed in 1322 (fourth line) and copied by his pupil John of Saxony in 1323 (fifth line in roman numerals).

AP5<h2>Another precious piece of text!</h2> In this small text we see the mention of a very important Parisian astronomer, John Vimond, 1️⃣ "Johannes vimundi” (first line).

AP5.1<h2>Another precious piece of text!</h2> John Vimond is the first to use Alfonsine astronomical parameters in the design of a table set in Latin, shortly before 1320. This small text is what we call an explicit (final words) of a work.&nbsp;The text, uniquely&nbsp;copied here, concerns an original instrument called “planicelium” and treats the daily motion of the sphere. It is only very recently that it was noticed by scholars, research are ongoing and many aspects are yet surrounded by mystery.

AP6<h2>John of Murs is also in the Manuscript</h2> This line mentions the name of John of Murs (“Tabula magistri Johannes de muris”), a very important Parisian astronomer of the early 14th century. With John of Lignères, John Vimond and John of Saxony, he is responsible for recasting the Alfonsine table in Latin. The manuscript thus collect works and mentions of the four main authors of the Parisian Alfonsine tradition.

AP6.1<h2>Fundamental arithmetic</h2> On this page we see a diagrammatic summary of Boethius De institutione arithmetica, a fundamental text of arithmetic. The presence of this text in John of Saxony student notebook is very interesting. It shows that learning astronomy was part of a broader training in the four liberal arts (arithmetic, geometry, music and astronomy) and indicates that theorical questions on numbers were also important for this group of Parisian astronomers at least.

AP7<h2>Learnig from shadows</h2> These three little diagrams represent the same instrument: a gnomon. This is probably the most simple astronomical instrument one can conceive: a vertical stick casting shadows on the ground. It is interesting to see how the same object is pictured in different ways. It is even more interesting if we understand that these different representations show the instrument as it should be used in a procedure described in the text nearby that allows finding the cardinal points and the meridian line of the place where the gnomon is set.&nbsp;The diagrams, as well as the texts, are copied by John of Saxony as he was learning astronomy from the text of his master, John of Lignères.

AP8<h2>The gnomon in a mathematical demonstration</h2> This diagram, and the small text that is just nearby to its right, concern the gnomon and work with shadows. It is a marginal annotation by John of Saxony to the text of his master, John of Lignères in Paris around 1323. The text and diagram provide a geometrical proof, mentioning several propositions of Euclid Elements, for two procedures described in John of Lignères text and allowing to connect the time of day and the length of the shadow. It is very rare to witness such grounding practices which might have been an integral component of advanced astronomy teaching in medieval universities.

AP9<h2>Non-Ptolemaic astronomy</h2> This diagram represents a non-ptolemaic planetary theory, that we call today “homeo-centric” because it aims at avoiding eccentric circles and replacing epicycles by small circles revolving at the surface of concentric spheres carrying the planets. Like Alfonsine astronomy, this alternative theory is of andalusian origin. It is the work of the 12th century astronomer al-Bitruji. Alfonsine theory of the motion of the star sphere shares some characteristic elements with al-Bitruji “homeo-centric” approach.

AP10<h2>Rules for multiplication and division</h2> The two little tables presented here concern multiplication and division, but not of numbers. They concern the units, or positions, with which sexagesimal numbers used in astronomical computation are composed. For instance reading the left hand side table shows that multiplying seconds by thirds one gets fifths, whereas reading the right hand side table one sees that dividing seconds by thirds the result is in minutes. These tables, by the hand of John of Saxony, may have been copied from al-Batani where they are also found. Here they are added to a treatise on sexagesimal multiplication by John of Murs. Astronomers' computations are not only complex and intricate, they rely on numbers format which are specific to astronomy.&nbsp;

AP11<h2>Book collector practices</h2> This is a table of content of the manuscript, maybe written by Amplonius, when the book entered his collection. Some of the main works composing the codex are listed and their content briefly commented. for instance, near (1) the word “bonus” noted as the last word of the third line from the bottom can be read. These types of notations are interesting because they reveal how the written records on which we based today historical research, were gathered and curated by the ancient.

AP12<h2>Intellectual counterpoint</h2> The text copied here, Pseudo-Ptolemy's Centiloquium, is a fundamental text of astrology first written in Arabic and translated several times to Latin. It often circulates with a commentary by an 11th century Arabic author known in Latin sources under the name “Haly”. This commentary is also copied in this manuscript. The marginal letters “p” (1) and “h” (2) mark the line in the text when Pseudo-Ptolemy Centiloquium and Haly commentary begin. In addition to this, a rubricated letter (i.e. marked with red ink) indicates the precise place in the line marking the alternance. This is one among many means at the disposal of medieval copyists to intertwine a text and its commentary: they were masters in the art of “intellectual counterpoint”!

Central part of the manuscript from the middle of the 14th and copied by John of Saxony's as he was the student of John of Lignères