[GeoffR]

One way to tell from the device if the book (ePub or KePub) has more than one chapter per file is that the tick mark on the table of contents does not track the reading progress properly. For example if chapters 1, 2, 3 are all in the same file then the tick will get stuck at chapter 1 and not advance until you reach chapter 4.

From Calibre you can explode the book and look at the toc.ncx file, or at the individual html files. I guess you need to be a bit familliar with ePub internals to quickly see what you are looking for though.

Usually doing an ePub --> ePub conversion in Calibre will cause the book to be split into one chapter per file. However in some cases where the publisher has done something unusual Calibre might not be able to recognise the chapter breaks and will need some help, and that can get tricky. Also doing an ePub --> ePub conversion can cause other problems such as preventing the line spacing from being able to be adjusted, so it is best not to do it unless you know you need to.

Most books I have come across have already been properly split into one chapter per file, only about 5% that need to be fixed. But I don't know if that is typical, it perhaps depends on what sort of books you read, which publishers, how old the books are etc.

I've attached a screenshot that shows the KePub reading progress popup. Note that the percentage at the top of the screen is for the entire book, while the other one is for the current chapter. In full screen mode you can also see the current page number by bringing up the <-> navigation menu (works for ePub and KePub.)

Edit: A warning: If you split the internal files or make other structural changes to the book in Calibre, then make sure you delete the old book from the ereader before using Calibre to send the modified one, otherwise the information in the device's database will not match the modified book and various strange things can happen.