Daniel Jeans improved the reliability of magnetic field mapping in the key4hep/k4geo repository by addressing a systematic error in coordinate transformations for detector simulations. He implemented a fix in C++ using Geant4, ensuring the x and y components of the magnetic field were correctly calculated from Br-Z field maps by applying cos(phi) and sin(phi) to the radial component, respectively. This adjustment aligned the simulation with standard coordinate conventions, reducing potential systematic errors and enhancing calibration fidelity. The work demonstrated careful attention to simulation accuracy and reproducibility, with all changes traceable to a specific commit for future reference and validation.