This effect can be seen in figures 5.4 and 5.5 . Figure 5.4 shows the output of detector 13 against time along with the wavelength of light falling on the detector. It can be seen that the detector output rises from a low state at the start of the observation, and that it does not fall back to its low level at the end. Realistically, only the down scan should be used. It is important to stress this - if you see your data is affected you must decide how much data to use and in extreme cases use only one scan.
Memory effects can also change the shape of line profiles.
As an example, as the grating scans across a strong gaussian line the sensitivity of the detectors will change. If this change is large enough it will result in one side of the gaussian having a detectably different shape from the other. If the scans are averaged the line will be broader than it actually is. Users should check for these effects and if they occur only use the unaffected half of a scan. The down scan has been shifted down by 500 Jy for clarity.