Desktop computers decline in value by 24% the moment they are sold, and notebooks' value declines by 20%, according to a study of more than 1,600 computers sold on eBay and the Dell website. This "age-zero" price drop accounts for much of the decline in value of used computers in the first few years; after that, prices decline further because of incompatibilities with newer technologies. At 5.5 to 6 years, a notebook has dropped to about one-tenth of its original price, say Christos Antonopoulos of the Greek Council of Economic Advisers and Plutarchos Sakellaris of Athens University of Economics and Business.