This article exposes certain functions of scientific correspondence during the second half of the 16(th) century. A professor of mathematics in Rome, Antonio Maria Pazzi, sends a mesolabe together with a letter to Barbaro, the humanist scholar of Venice. The latter would include parts of it in the Latin version of his commentary to Vitruvius. The analysis of the context of this publication shows that both arrive at aligning their personal intentions with the ideal of the "common good" by contributing to the spread of mathematical knowledge and practices.