Hi Robin
Worth looking at systemic difference between water and main lines…
I didnt get the part about switching between emission and absorption… All I do is enter the pixel-wise location of water and calib image lines into the table, having determined them from the combo image with no calibration. Then press ‘calculate polynomial’ and obtain the dispersion. I am not using Isis to actively seek the lines in the image. In this way I get a function that is fixed at both ends (and the centre). I do, however, then specify one of teh calib image lines as a reference point, but apparently this is optional with the ‘predefined dispersion’ option – you can put zero as the wavelength and it doesnt try and pick up any reference (at least that’s how I read it)
Kevin