(1)-REFS4U dan easyptr dan design4ptc^ dan saskia ptc^

http://www.refs4u.com/?ref=handokohan
http://easy-ptr.com/pages/index.php?refid=hbrow50

http://www.design4ptc.info/index.php?ref=bookface866

 http://www.saskiaptc.info/index.php?ref=hansbrow