Left-hand panel: comparison between local measurements [using Riess et al. 2011 and Humphreys et al. 2013 (dark blue, upper bar) and its reinterpretation by Efstathiou 2014 (light blue, lower bar)] and CMB-derived measurements of the Hubble constant from Planck+WP data (labelled as Planck) for several assumed cosmologies. The error bars correspond to 68 per cent confidence. The tension between the local and the CMB determinations is evident for some models (ΛCDM and OΛCDM) but not for others (wCDM or N_effΛCDM). The two measurements labelled ‘Planck ΛCDM’ refer to the Planck collaboration measurement (dark red, lower bar; Planck Collaboration XVI 2014b) and the re-analysis of Spergel, Flauger & Hlozek (2015, light red, upper bar). The bars in faded out colours represent reinterpretations of the original data sets represented in solid colours. Right-hand panel: the sound-horizon scale: its determination is virtually cosmology independent for cosmologies that differ on late-time history of the Universe, but the determination is extremely sensitive to uncertainties in the early (pre-recombination) history.