In the past six weeks, Amazon passed a major milestone: it now sells more Kindle books than printed books.

The statistic doesn’t come as a major surprise: by July last year Kindle book sales beat hardbacks, while in December they began outselling paperbacks. Now the Kindle outsells both paperback and hardback combined by a 105:100 ratio.

As usual, there are plenty of potential caveats. Leaving aside the fact that this is hardly representative of the entire book market, it’s not clear whether Amazon is including printed books sold through its Marketplace scheme, including second-hand titles.

Also, although the Kindle sales figure doesn’t include public domain books that are given away free of charge, there are plenty of titles (including many in the bestseller list for Kindle titles) that are around a dollar or even less. So it’s very likely that the revenue (if not the profit margin) from printed books is still much higher for Amazon.

One possible explanation for the apparent speeding up of the trend may be the recent release of Kindle with Special Offers, a version of the entry level Kindle that carries limited advertising and retails for $114, a $25 discount on the standard price. That’s proven something of a hit and is currently the best-selling electronic device at Amazon, so it may be that the overall number of Kindle users has had a significant boost.

There is some good news for lovers of the traditional printed page however: despite the changing proportions, the actual number of printed book sales is still on the rise, suggesting the medium isn’t going away any time soon.