I noticed this, too. If you take 16,000 words/day multiplied by 26,280 days (72 years' worth of days), you get the 420.48 million in the text. If you take tha

I noticed this, too. If you take 16,000 words/day multiplied by 26,280 days (72 years' worth of days), you get the 420.48 million in the text. If you take that number and multiply by 24, you get 10,091,520,000--close enough to 10 billion that I think the author made a days versus hours mistake somewhere. The remainder of the article seems to actually use the 420.48 million number and not 10 billion, as ringshall points out.