Members logged in

According to which criteria is the list of logged-in members compiled? I can't work out how it decides how to rearrange the sequence of names at the bottom of the front page.

I think it defaults to last click...

Although you have an option

I think it is ordered according to time of the last click, as the list given with the 'last click' option has a corresponding order.

Aaaaah, the mist clears.

Thanks.