This only works if you are very quick with your browsing of FT. If I visit at the end of the day, after going all day without reading, and I take a long time to do it, the unread stuff will eventually go out of whack. Right now, for instance, the unread stuff is already out of whack. Only the posts in the last little while are considered unread for me. Unless I visit multiple times a day, that happens on every visit.