Ussher's scheme is not accurate because these lists are not generational, but regnal, and the reigns of some kings coincided. Let us examine the problems with Ussher's scheme error by error.
They calculate the earth's age at 6000 years on the basis of ages assigned to these rulers.
Ussher failed to recognize that the so-called "genealogies" are King Lists.
They cannot be used to count generations because they are king lists and some kings ruled simultaneously, others ruled for short periods, and still others ruled for longer than a generation (40 years).
Error #2 Ussher did not recognize that some of the genealogical lists are telescopic. Such lists give the names of only the most famous rulers.
She married her cousin Methuselah and named her first-born son Lamech after her father.