Comparison between N/O derived from HCm and from different strong-line methods. At left, for all selected H ii regions, with the N2S2 parameter calibrated by Pérez-Montero & Contini (2009). At right, the calibration by Pilyugin & Grebel (2016) based on [N ii] and [O ii] emission lines for those regions whose [O ii] lines were used. Density of points over the mean value are represented according to the colour bar. The red solid line represents the 1:1 relation. The upper left crosses represent the standard deviation of the residuals to the direct method as carried out by Pérez-Montero & Contini (2009) and Pérez-Montero (2014).