http://books.google.com/books?id=xq9vzVKGeIgC&pg=PA62&lpg=PA62&dq=bent+gravers&source=bl&ots=pJAGq9ul3c&sig=G3HTOUw4TEOnnK-5JdNfNp2i698&hl=en&ei=H5kHTLrDKo-wNuWW1bUE&sa=X&oi=book_result&ct=result&resnum=5&ved=0CBQQ6AEwBDgK#
