This site uses dozens of pop-up windows for excellent educational and practical reasons. Many scientific publishers also use pop-ups for tables and figures. Some software (including the Google toolbar and Windows XP service pack 2) can block advertisements by intercepting pop-ups.
You will miss important information with the pop-up blocker running.
Users should switch off the pop-up blocker in Windows XP and disable the anti-popup feature in the Google toolbar. Better still, right click the Google toolbar and get rid of it completely, before using this web site.
Click the back button to return to the main site.