Update all existent callback panels on a page.

CallbackPanel1 contains a simple ASP Literal control that is updated with the server current time.
CallbackPanel2 contains a simple ASP Literal control that is updated with the server milliseconds.

CallbackPanel1 07:42:04.8289749

CallbackPanel2 828

For more information about CallbackPanel see How It Works page.
See also UpdateAllPanels tutorial.