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Chuck away the guidebook. You don’t need it any more. A revolutionary mobile-phone system is about to change sightseeing forever. It’s called Wikitude, and this is how it works.

You’re standing in a city, staring at a building. You suspect that it’s important and historic, but, frankly, you’ve no idea what it is. Instead of pulling out a guidebook, you reach for your phone and hold it up as if you were going to take a photo.

Here’s the clever bit. As you’d expect, the screen shows the building in front of you - but there’s a little logo at the bottom. Tap on it and it’ll tell you what you’re looking at. Ah, St Paul’s Cathedral. Knew it looked familiar.

Wikitude doesn’t stop there, though. Another tap will take you through to the Wikipedia entry for the cathedral - all 3,000 exhaustive words of it, as comprehensive and authoritative as the best guidebooks on the market. (A recent study in the journal Nature found that Wikipedia is up there with Encyclopaedia Britannica for accuracy.)

Wikitude is the culmination of five years’ work for its Austrian designer, Philipp Breuss, who calls the system “augmented reality”. It’s built to run on Google’s new Android operating system for mobiles - and the first phone to have that is the just-released T-Mobile G1, which uses GPS and triangulation to know exactly where it is and which way it’s facing.

Other models are expected to follow. You can see the implications.

Wikitude has 4,000 entries for locations in London. When your mobile will pick up every one in sight just by pointing, who needs a book? As long as it works, of course. To test it out, I took a hot-off-the-press G1 on a pleasure-boat trip up the Thames. Which would be more informative, the boat’s expert guide or Wikitude?

We steamed under Waterloo Bridge. “It’s faced in Portland stone, which is self-cleaning. You can tell that by how dirty it is,” was the guide’s only comment. Droll, but unhelpful. Wikitude, on the other hand, told me when it was finished (1945), what it was made from (yes, Portland stone), who designed it (Giles Gilbert Scott) and buckets more, including a juicy snippet on the assassination of Georgi Markov.

“To your right is Somerset House,” intoned the guide. Wrong: Wikitude correctly placed it on our left, filled me in on the history and architecture, and gave me a handy hint about the winter ice rink. And so it went on: all the way up one of the most historic waterways in the world, the human, clearly bored and wanting his tea, was comprehensively thrashed by the machine.

Not a fair contest, maybe, but Wikitude would have beaten anyone. St Paul’s, the bridges, Tate Modern - the phone identified them and had screeds on them all, and dozens more riverside sights besides.

My favourite was the entry on City Hall, helpfully noting that it’s been compared to Darth Vader’s helmet, a woodlouse and a glass testicle (by Ken Livingstone, no less). That’s the sort of detail I want from a guide.

It’s not perfect. In a city as thick with sights as London, your screen can be a confusing mass of dots, making it fiddly to hit the right one. As the boat cruised, the G1 got its knickers in a twist and needed rebooting to get its bearings. And, bizarrely, Wikitude didn’t have an entry on the Tower of London (though it did on the Jewel House inside). Overall, though, it’s a revelation.

For now, the biggest issue is cost. The system relies on internet downloads, which come free with your contract in the UK, but set you back upwards of £1.50 per megabyte overseas. Brussels is promising to force rates down for EU states. When it does, someone should warn the recycling plants - an awful lot of guidebooks are heading for the bin.

The G1 handset and Wikitude software come free with a £40-per-month contract from T-Mobile (0800 956 2208, www.t-mobile.co.uk ).

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