The upper plot shows the hyperfine splitting of the fine structure levels 3d⁶(⁵D)4s a ⁴D_7/2 − 3d⁵(⁶S)4s4p(³P) with allowed hyperfine transitions. The lower plot shows the hyperfine split profile of the transition observed in the uncalibrated laboratory spectrum at 12 975 Å, together with an indication of the positions and relative line strengths of the individual HFS transitions. A complete list of the Ritz wavelength and log (gf) for each HFS transition is available in Table 2.