Comparison between the O/H abundances derived from HCm with and without taking [O ii] emission lines. We only represent the H ii regions of the sample whose O/H uncertainty is reduced when [O ii] is considered. 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 cross represents the standard deviation of both methods in relation to the direct method as carried out by Pérez-Montero (2014).