The O2b line is extracted from ∼140 spectra of HD14943 taken during run 3 and the equivalent width (EW) is measured (illustration figure 2). The result is presented on the first figure as a function of time and airmass. Each night is distinguished by a different color and the size of the EW is normalized by the mean value of the run, times .1 to scale the axis. The observation strategy has been to take three images in a raw each time a given star was observed. As a result, it can be estimated that there is a fast varying component of the EW measurement which can be as high as 20%. This need to be study in greater detail, and images from Rasicam would prove useful.