Use the controls at the bottom of the book to zoom in and out with the magnifying glass icons, open the book full screen with the x-shaped arrows, and go directly to a certain page by double-clicking the page number it is on, editing the page number, and hitting enter.
Please note: The pages listed in the alphabetical index at the top of each digital volume differ from those on the handwritten pages inside the books. This is due to the index pages being counted as page numbers in the digital volume, but not in the original books.