Can someone help me to clear out a few questions about Intensity from spectral lines. - I have seen in many reports the unit cm-2 atm-1? Where does this come from? - What is the differences between line strength and the absolute intensity if the spectral line? - If you measure light from for example a flame with a FTS (Fourier Transform Spectrometer) What unit does the recorded spectrum have? Is this not possible to determine and you simply use arbitrary units. - Why is it difficult to measure absolute intensities?