B_RR² versus time and Potential Field Source Surface Flux estimates. As a function of time, black markers represent the most probable Parker spiral method value (at a one hour cadence) of the in situ heliospheric flux for each weekof data, the grey error bars represent the standard deviation with this week. The light gray and darker grey regions represent the full width half maxima of all PSM method measurements and all measurements within 0.3 AU respectively. A horizontal black line shows the most probable value (0.25 nT AU²) which is common to both the full and radius-restricted data sets (see Fig. 7). Blue (ADAPT-GONG) and red (ADAPT-HMI) curves show the open flux value predicted (see Eq. (1)) by potential source surface (PFSS) models using daily updating magnetograms over the mission. The solid (dashed) curves show results for 2.5 R_⊙ (2.0 R_⊙) source surface height, and the different colours differentiate the magnetogram source used.