The list shows both Leonardo's dilettantism in Latin and mathematics, and how printing changed the way we learn. Even in 1490, to learn "how to square a triangle", you did not have to get the master of arithmetic to show you. You could find a copy of Euclid's Elements and skim it up to Proposition II.14 [1]. The first printed edition of Elements (in Latin) was published in 1482 [2].

[1] https://mathcs.clarku.edu/~djoyce/elements/bookII/propII14.h... [2] https://archive.org/details/preclarissimusli00eucl