** Now, run '''IRAF - twodspec - identify''' on the corresponding raw 2D image. Select the same line and input its wavelength as just read off the plot. The solution is good to within a couple of Angstroms, and there are sufficient lines in the arcs that this should work well.
''Hint: remember that the raw and 1D Extracted spectra are flipped. A good trick is to reverse the plot window in IRAF with 'w' 'e' 'e' by selecting from bottom right to top left'''
** Repeat for several lines.
** When happy, automatically add all the lines (press "l").
<gallery>
plotIRAF1.png|python plot window next to IRAF identify window
plotIRAF2.png|After flipping IRAF identify window in x, it is now straightforward to match lines by eye
identifyAll.png|After matching ~5 lines, fitting, and pressing 'l' to auto-identify the rest
</gallery>
** Repeat for several lines.
** When happy, automatically add all the lines (press "l").
* Once you have identified the lines in one aperture, repeat for every nth pixel (probably every 5th pixel is fine, the tilt is about 0.6 pixels per pixel) using '''reidentify'''.
* Run '''fitcoords''' on the database produced by reidentify