Research Center Jülich is responsible for the design and construction of the High-Energy Storage Ring as a contribution to the future Facility for Ion and Proton Research (FAIR) at GSI in Darmstadt, Germany. In particular curved dipole magnets with a length of about 4.2 m are being manufactured, and their magnetic field should be characterized in terms of their multipole content. For these measurements we designed and built a mobile field mapper. It comprises eight triaxial Hall sensors, which can be moved along the curved center line of the dipole as well as rotated around it. Our contribution will highlight the design and first measurements with this new device.