Zoom on the C IV and Si IV regions for 0947+14 (SDSS DR12 spectrum), one of the two objects showing ultra-fast (> 0.1c) BAL signatures associated with C IV absorption, blue-wards of the Si IV emission line. Top panel: spectrum (blue line) and fit performed in IRAF; dashed lines indicate the position of the Si IV and C IV peaks as calculated from the redshift. Bottom panel: residuals between the C IV peak and −50 000 km s⁻¹, with absorption below 90% of the continuum highlighted in orange; dashed lines indicate the minimum and maximum velocity estimated for the BAL outflow.