Sawtooth instabilities cause sudden changes in the magnetic topology duringcombined neutral beam and fast wave heating in the DIII-D tokamak.Measurements with a motional Stark effect diagnostic provide accuratedetermination of the equilibria before and after the sawtooth reconnectionevents. The global magnetic helicity ∫A·B dV changes0.2±0.9% at a sawtooth crash. The local change in the helical flux,χ, is roughly consistent with the Kadomtsev model within large errors.The volume in which the helical flux changes is 85±15% of the volumepredicted by Kadomtsev, while the central value of χ is within 1% of thepredicted value.