When you're reading an eBook page by page, how do you scroll?

Which key (wheel, touch screen, strain gauge) are you pressing, which finger of which hand? How many words or what percentage of an A4 page appears/disappears in one action like click/tap? Maybe you have some non-trivial input devices involved in your reading process - pedals, encoders, maybe some camera is observing your face and a blink means one scrolling action? For an example of one of the different reading scenarios, let's imagine that you are reading a long detective story - you cannot skim the pages without delving into the meaning of each line, but this is not reading mathematical literature where you cannot skim the lines with your eyes without delving into the full picture of the meaning of each character.