[davidfor]

It isn't that Kobo can't count, it is that no one knows exactly what they are counting.

Firstly, the method for kepubs and epubs is different.

For epubs, it is probably pretty much just the page count, but, as that is calculated in a questionable way, it isn't perfect.

For kepubs, is not related to the page count at all. During the import, Kobo uses the internal file size to calculate a percentage of the full book for each chapter. That, plus a percentage for the beginning of each chapter, is stored in the database. When reading, the percent read at the beginning of the chapter will be displayed. And as you page through the chapter, the percent read is calculated within the chapter. This, I think, is done using the word count in the chapter. The graphs in the stats popup are done using the word count, so the percentage within the chapter is probably based on that.

And for the record, the word count for each chapter is calculated the first time a kepub is opened. It is stored in the database for use later.

The above is based on experimentation. I discovered some of it when playing with the stored word count. And some of it when doing the ToC updating in the Kobo Utilities plugin. And I have played with the different numbers in the database to see what effect it has. And all the numbers are stored as integers, so there are also rounding errors happening.