Radial magnetic field at the CMB for six equally spaced epochs from 1840 (top) to 1990 (bottom), for models built using (a) quadratic regularizations in space and time, (b) a quadratic temporal regularization together with a maximum entropy spatial regularization, and (c) maximum entropy regularizations in space and time. For all the snapshots the colourbar ranges from −1 mT (dark blue) to +1 mT (dark red), with contours every 50 μT.