Mode of access: Internet from the Internet web site. Address as of 11/15/05: http://www.cr.nps.gov/hps/tps/briefs/brief07.htm; current access via PURL.
Title from title screen (viewed on Nov. 15, 2005).
"The web versions of the Preservation Briefs differ somewhat from the printed versions. Many illustrations are new, captions are simplified, illustrations are typically in color rather than black and white, and some complex charts have been omitted."