There are three distinct ranking schemes on Amazon: one for the top selling 10,000 books, another for the books between 10,000 and 100,000, and a third for ranks above 100,000.
Note this estimate:
Rank / Copies per day
1 / X
10 / 100
100 / 30
1000 / 10
10,000 / 2 (11 copies every 5 days)
100,000 / 1 copy a week
1,000,000 / around 15 total, depends on pub date
2,000,000 / around 2 total, depends on pub date
