* [https://web.archive.org/web/20130616220554/http://www.pentrace.net/penbase/Data_Returns/full_article.asp?id=406] Giovanni Abrate article on Pen Trace | * [https://web.archive.org/web/20130616220554/http://www.pentrace.net/penbase/Data_Returns/full_article.asp?id=406] Giovanni Abrate article on Pen Trace |