During their recent work on the TUDelft-MUDE/book repository, I.C. Slingerland focused on improving the accuracy of physics learning materials by correcting a key mathematical formula in the Exercise section. Using Jupyter Notebook and leveraging their background in physics and technical writing, Slingerland identified and fixed an error in the application of the Divergence Theorem, replacing an incorrect surface integral with the appropriate volume integral. This targeted bug fix was carefully documented and integrated as a small, stable patch, ensuring the codebase remained robust. The update enhanced the clarity of instructional content and reduced the likelihood of student confusion.