http://www.nikonians.org/html/resources/non-nikon_articles/markins/index.html
http://www.earthboundlight.com/phototips/perfect-tripod-head.html
http://www.naturephotosociety.org.sg/ASP/Article.asp?DBAPublishDate=7/1/2004
http://www.earthboundlight.com/phototips/perfect-tripod-head.html
http://www.naturephotosociety.org.sg/ASP/Article.asp?DBAPublishDate=7/1/2004