The relationships between the metallicities obtained from the five calibration methods once converted into the PP04 O3N2 base metallicity (blue open circles). The 1:1 line is shown in red and the unconverted metallicities from each calibration are shown for comparison (grey open circles). The scatter, σ, is the standard deviation of the residuals, δ, between the two plotted metallicities converted into the PP04 O3N2 base metallicity, and is the mean of these residuals.