Depending on your trust in the stats thrown out by mobile advertising companies, the ticker on Chitika's website could be very useful or a pile of PR tomfoolery.

The online advertising service, which claims 2 billion monthly impressions across more than 80,000 websites, is tracking iPad second by second.

It currently estimates the number of devices in the wild is just under 500,000 - 493,957 as I write.

Beans in a jar

More interesting perhaps is the way it calculates this number.

It counts how many iPads it sees on its network and then multiplies that up by the proportion of the internet it thinks it sees at any given time.

Of course, one limitation concerns how many people are taking their iPads online. Chitika points out, "We've also learned that the wi-fi iPad may not be seen as primarily an internet surfing device".

To that extent, until we get the next sales update from Apple to cross reference, it's perhaps sensible to take Chitika's estimate with a pinch of salt, or use it as a measure of sales growth rather than an absolute figure.

[source: Chitika iPad Stats tracker]