Hi Vijay, It has been about a year since I reduce any GRIM data, but I will try to give useful advice. First off, I have never found that I could use the offsets in the headers to align my images. Now, I never bothered guiding either, but I would be wary of trusting them. The package I used was DIMSUM (which has been IRAF-ified and is called xdimsum). DIMSUM creates a first pass image that does a good enough job at sky subtraction for you to mark bright stars for alignment purposes. As for recent flats, readnoise values and bad pixel masks, I would suggest waiting for a reply from someone who has used the instrument this century and not that last.... cheers Brad APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 47 in the apo35-grim archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-grim/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-grim@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO