These calendars are using projected dates. We will not know the true dates until certain things take place. The new moon is sighted to officially start each month. The year starts as certain signs are revealed in nature. The grape vines begin to flower, doves start nesting, fig trees start to form green figs, grapes give off the smell of the sour grape in the bud, and on and on. These are listed in the Song of Solomon 2:12-13 as just one of the many scriptural patterns which address the change from winter to summer in Israel. The barley reaches a state of maturity that falls between the agricultural terms of soft dough and hard dough. This is the barley plant maturity that is required to have a "Wave Sheaf" offering 2 weeks later. The Week of Unleavened Bread begins 2 weeks after the first day of the year. Traditionally this stage of plant maturity was called "AVIV". As one searches back even further in the Bible you discover the Passover Festival Week is originally called the "Time of Life" - the time of renewing covenant with YEHOVAH.