In the low-D mode, ESI spectra are similar to any long-slit spectrograph, with two differences: the spectra are tilted by 6.5 degrees with respect to the CCD rows, and the night sky lines are more highly curved than in most spectrographs.
The quickest way to get a quick look at the low-D frames is to use IRAF to rotate the frames and then use the usual FIGDISP row plot tools (or alternatively IRAF itself).
In a window with IRAF running, cd to a scratch directory with the frames. To create a copy of an image (say ``esi0001.fits'') that is rotated such that a source spectrum runs along CCD rows, use the following command:
cl> rotate esi0001 rot0001 rotation=-6.5 interpolant=spline3
This leaves esi0001 unchanged; rot0001 is the rotated frame.