World's oldest printed book.

What is the world's oldest printed book? The question came from one of my friends casually. To be very honest I failed to answer.While reading today's Newspaper I suddenly came across that same question and fortunately got the answer. It says that the oldest printed book's date is May 11th 868.It was a Chinese translation of Vajracchedik Prajnaparamita Sutra from Diamond Sutra.It is consider as the world's oldest printed book. A monk who got it from the 'caves of thousand Buddhs' sold it to a British archaeologist in the year 1907.