Upper panel: reionisation histories compared to low-redshift probes. Shaded envelopes show the low/high-τ values derived from Planck with uncertainties. The red line indicates the best Planck value τ = 0.66. Dashed lines are derived from the best ionisation rate (Ṅ_ion) of ISHI15, ROB15, BOU15. Symbols are current constraints from direct line-of-sight measurements compiled by BOU15. Middle panel: corresponding ρ_SFR for Planck and the best fit of ROB15 with observational data compiled by ROB15. The grey dashed part corresponds to Q_HII ~ 1. Lower panel: evolution of the integrated optical depth for the different studies plotted in the upper panel.