Maximum-entropy reconstructions of the large-scale magnetic topology of τ Boo as derived from our 2008 January (second column), 2008 June (third column) and 2008 July (right-hand column) data sets are displayed. The radial, azimuthal and meridional components of the field (with magnetic flux values labelled in G). The star is shown in flattened polar projection down to latitudes of −30°, with the equator depicted as a bold circle and parallels as dashed circles. Radial ticks around each plot indicate orbital phases of observations. The 2007 June magnetic map of τ Boo (Donati et al. 2008) is added in the left-hand column to ease comparison.