Just want to make sure I am understanding correctly, when a book is bought or downloaded say from Amazon, the author gets a little money? If true that is good to hear!
If I'm not totally mistaken he/she only gets extra money if/when their advance has been topped by the royalties he would have gotten if there hadn't been an advance.
Note: the following numbers are just made up by me, no idea how the real numbers look like
Let's say Christopher would get a 5000 $ advance for his latest Trek Book, and would get 0,40 $ royalties on any book sold, he wouldn't get any additional money until the 12,501st book is sold.