The K3 has a cool feature I like in that the location/progress bar also shows where the chapters/sections are located, assuming the mobi was formatted correctly. This gives you a bit of visual as to where you are in the book and the chapter. The K4, K5, and K6 no longer have this feature. In the K3, K4, and K5 the location/page number is always visible when reading a book. The K6 auto hides the location/page number.