where, over a fixed velocity increment, the blue NAC region is relatively homogeneous and decoupled from the rest of the wind. An important example is the NACs seen in the C[iv]{} $\lambda\lambda$1550 and N[v]{} $\lambda\lambda$1240 lines of weak-wind main-sequence late O-type stars (e.g. Kaper et al. 1996). The mass-loss determinations in these weak-wind cases remain a challenge for the line-driven wind theory (e.g. Bouret et al. 2005).

[llll]{} & & &\
&(blue NAC) & (blue low-vel) &\
& (10$^{-9}$ M$_\odot$ yr$^{-1}$) & (10$^{-9}$ M$_\odot$ yr$^{-1}$) & ( 10$^{-6}$ M$_\odot$ yr$^{-1}$)\
\
HD 13866 & 10.61 & 1.21 & 1.13\
HD 47240 & 15.82 & 3.40 & 1.82\
HD 111990 & 6.35 & 1.95 & 1.35\
HD 51309 & 1.88 & 2.25 & 1.10\
HD 36371 & 2.60 & 0.89 & 1.42\
AV 264 & 3.10 & 2.41 & 10.50\
\
HD 91316 & 5.69 & 1.32 & 1.81\
HD 191877 & 4.06 & 1.29 & 1.55\
HD 93840 & 3.26 & 1.09 & 1.65\
HD 100276 & 2.38 & 1.94 & 3.54\
HD 152234 & 3.04 & 2.43 & 3.40\
HD 224151 & 2.07 & 1.17 & 0.17\

![Examples of SEI fits to the weak C[iv]{} $\lambda\lambda$1550 P Cygni doublet 