Every one of Germany's 82 letter sorting centers uses sorting machines that work according to a principle invented by Dr. Wolf-Stephan Wilke. These large-letter sorting machines use a special arrangement of pocket carousels that move above the containers into which the letters are sorted. Thanks to this arrangement, the letter throughput is dramatically increased without the need for more space. These modern sorting systems have also attracted attention from postal services outside Germany. Wilke works at the Infrastructure & Cities Sector in Konstanz, Germany.