Aharon Ben Meir
In the year 4681, a dispute erupted between Aharon Ben Meir, Nasi of the Sanhedrin in Eretz Yisrael, who insisted that Molad Nissan of year 1 should be on Wednesday at 9 hours exactly, at 4:9:0, and Rav Saadya Gaon, of Bavel, who insisted that Molad Tishrei after that, was on Friday, at 14 hours exactly, at 6:14:0 (and at 2:5:204 - BaHaRaD - one year earlier). The two differ by 642 Chalakim. That is, according to Rav Saadya, Molad Nissan is at 4:9:642. In the end, Ben Meir seems to have given up and since then the Halacha is according to Rav Saadya.
About what was the dispute? Probably, Ben Meir and his tradition felt that Nissan was more important than Tishrei. Is Nissan not the first month? But, let us be fair. To insist that either Molad Nissan or Molad Tishrei of year 1 or 2 must be a round number, is nonsense. When he was excommunicated by the exilarch of Bavel, Ben Meir could have repaid in kind, but he did not, in the end. He must have understood that, as Israel was in the exile, it was of importance to have one Calendar, no matter how arbitrary.
One could ask what is the Halacha according to the truth. In truth, there is no Halacha. In exile, there should be one Halacha, the details of which are not important. The truth remains Bachuts (to the Talmud Bavli), where Ben Zoma is (Chagigah 15a). Note that Ben Zoma is already Bachuts to the Talmud Yerushalmi (Chagiga 2:5). The one Halacha of the exile started breaking down, around the year 5600, when the spirit of Ben Zoma was, as it were, revived with the Haskala movement.
We have named the Molad-fixing term after Ben Meir, who wanted to subtract 0:0:642 where we subtract the Ben Meir term, z/2. In order to honor Aharon Ben Meir, who led go of his "truth," in order for Israel to survive, so that a bigger truth, could be revealed at the end of the exile. It is possible to say that such is the truth of Shim'on Ben Zoma, which shook the world (Bereshit Rabbah 4:6), and Aharon ben Meir had a hunch of it.
About what was the dispute? Probably, Ben Meir and his tradition felt that Nissan was more important than Tishrei. Is Nissan not the first month? But, let us be fair. To insist that either Molad Nissan or Molad Tishrei of year 1 or 2 must be a round number, is nonsense. When he was excommunicated by the exilarch of Bavel, Ben Meir could have repaid in kind, but he did not, in the end. He must have understood that, as Israel was in the exile, it was of importance to have one Calendar, no matter how arbitrary.
One could ask what is the Halacha according to the truth. In truth, there is no Halacha. In exile, there should be one Halacha, the details of which are not important. The truth remains Bachuts (to the Talmud Bavli), where Ben Zoma is (Chagigah 15a). Note that Ben Zoma is already Bachuts to the Talmud Yerushalmi (Chagiga 2:5). The one Halacha of the exile started breaking down, around the year 5600, when the spirit of Ben Zoma was, as it were, revived with the Haskala movement.
We have named the Molad-fixing term after Ben Meir, who wanted to subtract 0:0:642 where we subtract the Ben Meir term, z/2. In order to honor Aharon Ben Meir, who led go of his "truth," in order for Israel to survive, so that a bigger truth, could be revealed at the end of the exile. It is possible to say that such is the truth of Shim'on Ben Zoma, which shook the world (Bereshit Rabbah 4:6), and Aharon ben Meir had a hunch of it.