The status bar displays the Document window’s current dimensions (in pixels). To design a page that looks its best at a specific size, you can adjust the Document window to any of the predetermined sizes, edit those predetermined sizes, or create sizes.
The window size shown reflects the inside dimensions of the browser window, without borders; the monitor size is listed in parentheses. For example, you would use the size “536 x 196 (640 x 480, Default)” if your visitors are likely to be using Microsoft Internet Explorer or Netscape Navigator in their default configurations on a 640 x 480 monitor.