Hillel the Nasi, grandson of Rabbi Yehuda Nesia grandson of grandson of our Holy Rabbi, was the tenth [in line] from Hillel the Elder, and until his time they sanctified [the new month] based on sighting. So writes the Rambam in chapter 5 of the Laws of Sanctification of the New Moon, and the Ramban in his Responsa on the Counting of the Commandments, section 152, and in the book Yesod Olam, section 4, chapter 9, and he arranged the calculation of the calendar cycle as it is practiced today.
And this was in the year 670 [(i.e., according to the Seleucid era, and so it says in Shir HaShirim, page 38, section 2)], 360 years after the destruction, which is the year 4118 of creation. [And in Shir HaShirim, pages 21 and 35, section 71, it is written in the name of Yesod Olam that it was the year 460, that is 200 years after the destruction, but this is a scribal error, for 200 after the destruction is the year 4128, so how did he write year 460? And furthermore, in the year 460 there were Rabban Sevarai, and see Yuchsin in the order of Amoraim, letter 2, may his memory be for a blessing, the Geonim mentioned this order: Our Holy Rabbi and Rabban Gamliel his son and Rabbi Yehuda Nesia his son who established the calendar cycle, and Rabban Gamliel son of this Hillel, and Yehuda his son, and Rabban Gamliel in Tiberias in the year 530 according to the Seleucid era.
And so it is written in Shir HaShirim, page 35, section 2: I saw in Yuchsin that Rabbi Hillel had a son whose name was (should say: whose name) Rabban Gamliel, and he had a son whose name was Rabbi Yehuda, and he had a son whose name was Rabban Gamliel in Tiberias in the year 830 according to the Seleucid era, end of quote. And there is a scribal error in Yuchsin in what it says "and Rabbi Yehuda Nesia his son who established the calendar cycle," which implies that Rabbi Yehuda Nesia established the calendar - this is an error, for Hillel his son established the calendar, and what it says "and Rabban Gamliel son of this Hillel and Yehuda his son and Rabban Gamliel in Tiberias in the year 530" also has a scribal error, for we do not find that Hillel had a son named Rabban Gamliel.
But what it says "and Yehuda his son" means the son of Rabban Gamliel son of Hillel - we also do not find him, and it should read: Our Holy Rabbi and Rabban Gamliel his son, and this is Rabban Gamliel in Tiberias who was truly in the year 530 according to the Seleucid era (see above) and Rabbi Yehuda Nesia son of Rabban Gamliel, and Hillel son of Rabbi Yehuda Nesia who established the calendar, and the rest is a scribal error, and it is easy to understand.] And in his days the ordination ceased in the Land of Israel [(Tzemach David). And Shir HaShirim wrote, page 154:] that from then they returned to counting from creation rather than from the Seleucid era.