You probably want to use cookies, but just for variety, here are some more possibilities:

You could process the pages with your script and insert the variable into the HTML as a hidden form field, but this leaves it open to manipulation. Another possible solution is to write the variable to a file linked to the user's IP address or a combination of any two of these: write the variable to a file linked to cookie data you set in the user's browser, etc...

SpaceAce