Seven extra lunar months were the chosen standard practice that matched with the seven-day week. Middle Eastern calendars likely intercalated 7-months as 209-days of l/s separation time. The 360-day length of year was common in very early prehistory. Extending the single l/s calendar year to the Mayan katun 20-year multiple of the l/s calendar continues exactly this fundamental, approximate intercalation of 210-days. Any l/s calendar year of 360-days balances the difference between lunar years and solar years. The outcome is time split to become 105-days each for the lunar-side and solar-side.
Moon as the Earliest Calendar give readers of the Holy Bible information recorded in ancient times. Lunar/solar calendars were common throughout the ancient world. Three calendar systems that help our study of Bible times are the Jewish, Mesoamerican and the Egyptian calendars. Changes in the appearance of the moon at night provide the seven-day week. Time steps in the lunar/solar calendar accumulate for longer time cycles.