What is "septuagint chronology"

Septuagint \Sep"tu*a*gint\, n. [From L. septuaginta seventy.] A Greek version of the Old Testament; -- so called because it was believed to be the work of seventy (or rather of seventy-two) translators.

Note: The causes which produced it [the Septuagint], the number and names of the translators, the times at which different portions were translated, are all uncertain. The only point in which all agree is that Alexandria was the birthplace of the version. On one other point there is a near agreement, namely, as to time, that the version was made, or at least commenced, in the time of the early Ptolemies, in the first half of the third century b.c.
--Dr. W. Smith (Bib. Dict.)

Septuagint chronology, the chronology founded upon the dates of the Septuagint, which makes 1500 years more from the creation to Abraham than the Hebrew Bible.