They're not rising -- those are not sales per year, but the *total* number of sales since the book went on sale.
I've been doing it that way for a couple of reasons. One is that I have the total since a book went on sale already there on the spreadsheet and don't have to separately calculate "this year's sales". The other is that the total ever sold is of interest to ebook authors - as noted in the post, it's of interest in making commercial decisions about continuing a series or focusing on a particular genre.
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Date: 2011-12-27 08:19 am (UTC)I've been doing it that way for a couple of reasons. One is that I have the total since a book went on sale already there on the spreadsheet and don't have to separately calculate "this year's sales". The other is that the total ever sold is of interest to ebook authors - as noted in the post, it's of interest in making commercial decisions about continuing a series or focusing on a particular genre.