Six related problems in calendrical study are addressed. In Chapter 2, the West, inheritor of Rome, is seen as solar-calendrical, unfamiliar with Hebrew calendrics apart from the Church's specialised use of a luni-solar calendar for Paschal calculations. Ancient calendars were usually lunar-based, although most periodically synchronised with the seasons (luni-solar). These models are reviewed. In Chapter 3, ANE and Mediterranean calendars show improved international astronomy - historically, the province of priestly astronomers. Yet, in Chapter 4, the third problem is that Mishnaic and Talmudic evidence speaks of strict observance of New Moons and <I>ad hoc</I> intercalation. If mathematical schemes for the lunar month were in operation in the Hebrews' <I>milieu</I> by 380 BCE, why were they so far behind in rabbinical times? The solution is: they deliberately chose to rely on observation. This cannot exclude an earlier, more mathematical tradition (Segal, 1957). The fourth problem, in Chapter 5, is the 364-day solar calendar, associated with Jaubert (1953, 1957), supported by VanderKam (1979), and Davies (1983). By acknowledging the comparative calendrical realism in the <I>Mishmarot</I>, luni-solar and solar evidence is examined in the Primeval History where Creation and Flood evince synchronistic ideas. The fifth problem, in Chapter 6, is the 'Key of Enoch', the idea that Enoch's full age in Gen 5:23 represents 365<I> days</I>. It is shown that <I>Gen 11:10-26 contains a synchronistic calendar of 6 years and 84 years, </I>similar to that hypothesised by Glessmer (1996) for the <I>'Otot</I>. This covert scheme is called Genesis 11 Synchronistic Calendar. The sixth problem, in Chapter 7, is the pre-history of <I>Qumran's</I> synchronistic calendars, which the Genesis calendar illuminates. A failure to recognised the <I>covert calendrical genre</I> was caused by unfamiliarity with ancient calendrics, and a traditional reading of P's genealogies.