How fluther knows how many people observing right now my question or answering it in a real time?

Still do not understand how it works.

After all, Web sites built on the call server and returns an HTML answer. How static HTML page knows how many people are watching right now the page in a real time?

Well, If I am asking the server for question A, than it knows I’m now observing question A, but after a while I leave this page and go to another one or I can just close my browser. How fluther knows when I have stoped to observe question A?