Does there exist any digital copy of the original article (or a transcript) K. Levenberg, A method for the solution of certain problems in least-squares, Quart. Appl. Math. 2 (1944): 164-168?
It is (obviously!) cited in numerous works, but the paper itself appears to have completely vanished. There seems to be not even any publisher, library, etc. proposing to buy a hard copy or anything alike. Apart from the citations all over the places, the paper has ceased to exist?!
This link might be better. The paper is now open access and the pdf is searchable.