That is the key to unlocking the CORRECT algorithm of genealogies versus chronologies.
The Patriarchs were God's mediators lords and judges on the earth. Hebrews would date their calendars by the reginal years of the patriarchs (for example the dating of the flood). The concept here is to SUM the
entire lifespan of the patriarchs.
Undoubtedly there were MANY more than 4 father-son generations during the 430 years sojourn.
Nevertheless the Bible only indicates four. God Himself only prophesies four. This is not at all an accident.
Now I do not vouch for every detail of this link. There are errors but they are not that significant. Nevertheless, what the author postulates is absolutely correct. And don't jettison the content because of the reputation of this author. Everybody knows about him so please don't comment.
Usshers chronology is worse than useless. The Masoretic text is erronious, undoubtedly being edited by rabbi Akiva. One must use the only copy we have of the Alexandrian LXX. The date of creation is pushed back to beyond 11,000 BC. Which completely solves the outrageous problem of Abraham being born so soon after the flood.
www.biblemysteries.com/library/adam.htm
Levi: 77 years in Egypt
Kohath: 133 years in Egypt
Amram: 137 years in Egypt
Aaron: 83 years in Egypt
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430 years total time
"Turning now to the Biblical record, we discover the following interesting information in Exodus 12:40-41, "Now the sojourning of the children of Israel, who dwelt in Egypt, was four hundred and thirty years. And it came to pass at the end of the four hundred and thirty years, even the selfsame day it came to pass, that all the hosts of the LORD went out from the land of Egypt." God thus shows us clearly that the calendar used to record the passage of time during the Egyptian sojourn was based on the lives of Levi and his descendants, Kohath, Amram, and Aaron. This also explains the prophecy given to Abraham in Genesis 15:13-16, that his descendants would be oppressed 400 years (they were not oppressed during the beginning of their sojourn) in a land that was not theirs, and that they would return to their own land in the fourth generation."