Here's a quick report for all you Harry Potter fans. We've just spotted that a rare first paperback edition of Harry Potter and the Philosopher's Stone today sold for £320.

The slightly battered copy's condition report mentioned browning to the book's margins, creases to its covers, rubbing and some peeling of its cover laminate.

Still, it's fascinating to think that this book is today worth £320 when, just 15 years ago in 1997, you could have bought it for 1% of that price in a book shop.

The first hardback edition of the Philosopher's Stone is especially rare. It had a print run of 500. Four hundred went to public libraries, leaving only 100 on sale to the public.

Consequently, hardback copies of Harry Potter and the Philosopher's Stone are more valued at auction.

And, in addition to rarity, it's amazing what an autograph can do for a book's value.

Harry Potter First Editions, and JK Rowling's signature, have soared in value

Back in February 2010, a copy of Harry Potter and the Philosopher's Stone signed and inscribed by author JK Rowling brought $24,000 at a US auction.

Again, compare that to the value the book would originally have sold for in 1997.

JK Rowling's autograph: among the market's best performers

As reflects her rapid ascent from penniless single mum to wealthy author, the average value of Joanne Rowling's signature rose by 279.7% between 2000-2011.

In other words, a signed Harry Potter book worth £395 in 2000 may have risen in value to £1,500! And as for what the same book could be worth in another 11 years...

We presently have another Rowling-signed Harry Potter book for sale, here at Paul Fraser Collectibles.

This is a hardback, first edition copy of Harry Potter and the Chamber of Secrets, the second novel in the series, published in 1998. JK Rowling has autographed the book herself. You can find out more about it by following this link.