Part of the digital lead is probably attributable to the fact that the hardcover version has been available for longer than the digital copy; the print The Lost Symbol already spent 150 days as one of Amazon’s top 100 books in the thriller category, compared to the Kindle copy, which has held the top spot for just two—meaning demand for the print version could already be satiated.

There’s also the pricing factor; the hardcover book costs more—and users have to pay for shipping. Fast Company’s Kit Eaton also questions how the book’s Kindle sales would stack up against retail figures from across the board, since data from stores takes longer to update than Amazon’s real-time Kindle stats.

Caveats aside, the fact that a best-selling author is at least temporarily selling more copies of his book digitally than in hardcover only adds to the flurry of activity around e-books, from new product announcements, to M&A deals, to price wars.