The most important instability is the variation of refractive index of the air inside the spectrometer due to temperature fluctuations. Another effect of the temperature fluctuation is the issue raised in Slide 8 regarding steering of the source image on the detector element. The saturation of a cryogenic detector can drift if the source image position fluctuates. Even the beamsplitter efficiency varies with temperature. The last three items in this list are also likely instabilities, but beyond the scope of this talk.