The “decimal theory” is that the ages of the OT ancients had a decimal missing. For example, Methuselah wasn’t 969 when he died, he was 96.9 years old.
Decimal missing?
Only in English. The Hebrew uses words, not numerals. Read Genesis 5. Enoch sired Methuselah at the age of 6.5?
So then the New Eathers are off by a factor of ten too? Then the Earth must only be 400 years old.