Mean value (left column) and normalised standard deviation (right column) for the ratios as a function of the energy of the upper level of the radiative transitions. The intensities are obtained with the STS CRC Dubernet et al. (2009) and Daniel et al. (2011). The transitions that involve an upper energy level that is the backbone are indicated by blue points. The transitions where the upper level is not a backbone level while the lower level is backbone are indicated by red points.