There's no question the Swedish Treskilling Yellow is the world's most valuable stamp. The last time it was on the market it sold for a healthy US$1.9 million.

　　But swedish researchers said yesterday the stamp is worth even more if one goes by weight.

　　The swedish National Testing and Research Institute measured for the first time the stamp's exact mass, volume and density and worked out its value per kilogram.

　　Since the stamp itself weighs just 0.03 grams, and using the purchase price as the measure, then the stamp is worth a whopping 562 billion kronor (US$76 billion) per kilogram.

　　That's not to say the stamp is actually going to be sold for that sort of money. Philatelists base a stamp's value on its rarity, color and condition, not its weight, real or projected.

　　But zurich-based Stamp Collection AG commissioned the research as part of a book it is publishing about the stamp's history and its different owners through the years.

　　The book, "The Three-skilling Yellow," is expected to be released in Europe and North America in December.

　　"The stamp is a true legend. The book will help us bring an important part of the Swedish national heritage to audiences all over the world," Hans Lernestaal, the company's chief executive said yesterday.

　　The three-skilling denomination series was Sweden's first stamp issue and was normally printed in a greenish color. A skilling was the hundredth of the daler, Sweden's former monetary unit.

　　Printed in 1855, it was used on an envelope two years later.

　　A swedish boy discovered the stamp in 1885 in a pile of letters left by his grandparents. Over the years, it has since changed hands several times with its value increasing steadily.

　　(The Associated Press)