Good spotting igorsk.
Thinking about it, holding 1 goes to the start and holding 0 goes to the end - that leaves 8 buttons left to jump to places within the book.
It seems
2 goes to 11%,
3 goes to 22%
4 goes to 33%
5 goes to 44%
6 goes to 55%
7 goes to 66%
8 goes to 77%
9 goes to 88%
