[HarryT]

I've also no idea. I've completely lost track of what reading devices I've owned, other than that it's well into double figures. All I can say is that in the last few years I've bought a new readers about once every 2-3 years, and that I typically read 100-120 ebooks a year, so I probably average somewhere around 200-350 books per reader. When devices were evolving rapidly, the number read per device would have been significantly lower.