Ernst Wilhelm Forstemann was the royal librarian at Dresden, not a Mesoamericanist, and he had the codex in front of him. Working in the 1880s he broke the numeration, the bar-and-dot system, the shell sign for zero, the place value running in twenties with a break at the third position, and from it reconstructed the Long Count, the absolute chronology by which the Maya dated events from a fixed zero point. He identified the Venus table for what it was and worked out the architecture of the eclipse table. All of this was done half a century and more before the phonetic values of the script were established: the Maya could be read as mathematicians and astronomers long before they could be read as speakers of a language.
The same work began the codex's least useful legacy. Forstemann described the final page as a picture of the destruction of the world; Sylvanus Morley repeated and amplified that reading, and through his widely read survey of 1946 the flood page entered popular circulation as Maya apocalypse. When the thirteenth bak'tun of the Long Count ended in December 2012, the two were welded together in books, films and television, and the Dresden Codex was cited as the ancient authority.
There is nothing in it. The flood page carries no date and no reference to any bak'tun ending. The Long Count did not stop in 2012; Maya inscriptions record dates far beyond it, and a text at Palenque projects forward to a date in the year 4772. Mayanists said so consistently for years and were consistently ignored. The codex records a calendar built to keep running, not to expire.