passing variables with HTTP_GET_VARS

Can someone show me a simple example of how to make variables availble to all pages in my site via $http_post_vars and $http_get_vars. just say I have a page index.php and that is doing a calucualtion and creating a couple of variables called $age and $height. How so I make these variables globally available and how do all the other pages show/retrieve them?? Many Thanks AD