If you want it to remember across sessions, you'll need cookies.
You could stash it in the querystring of the view records page(s); if you're using a link to page through, then you can manually echo it in the URL as part of a querystring. When the page is hit, check to see if the value is set and if so use it, otherwise use some default value.
The drawbacks of this method is that (a) it quickly becomes messy if you want anything else remembered, and (b) it is only remembered for the duration that they're viewing the results page - if they leave it and come back it will revert to the default value.
Otherwise I'd use either sessions or a cookie.
