...it...doesn't work that way.
Okay. Now interested in how it does work. If someone doesn't log out, how does it not effect the online numbers.
Member A logs in. Member A looks at a few pages, then closes the window and walks away.
From Member A's perspective, he's still logged in, but the server only "challenges" - checks login credentials - when they request a page.
So, Member A comes onto the site, opens a thread and reads it. Now, say he's reading it for 15 minutes
without changing page - from the sites point of view, he's not online, because he's not made a page request in fifteen minutes, so he'll drop off the "Who's Online" list.
Whether or not you are logged into a forum isn't stored there - the login credentials are stored locally, on your machines (which is what Cookies do).
It doesn't have to be fifteen minutes, I'm just going by AFF's setting.