Kryptos : K2. What is the origin of the “abscissa” keyword?
I think the best theory is crib-dragging the phrase "virtuALLYINVISIBLE" from the morse code sections. This will line up with "itwastotALLYINVISIBLE" from K2 and reveal the entire keyword, repeating and removing any doubts.

Come to think of it, it may very well have been the intension of Sanborn to have us decode K2 first by this method, and then from K2's ending (IDBYROWS/XLAYERTWO) derive the word palimpsest, because that´s basically what it is. One text scraped away to make room for another text and hinted at by the use of "LAYER TWO".