Well, that all depends - and I warn that what I'm about to explain can get complicated.
The "Show unread posts since last visit" feature does exactly that - it shows the posts made between the time someone leaves/logs out of the forum and the time they return/login. And by that I specifically mean the time they switch their browser to another Web site (without having the forum still opened in another tab/window of their browser) or they close their browser entirely and the time they surf back to the forum or they open their browser again and return to the forum. However, if after reading posts someone's browser remains open and logged into the forum and additional posts are made that they don't read before they leave/logout, those posts will not show up the next time they return/login and use "Show unread posts since last visit" because those posts were made before their last visit ended.
A way to try to see if someone does indeed have any unread posts is to use the "All Unread Topics" feature of the "Show unread posts since last visit" feature, the link for which is in the bottom right hand corner of each page of the feature, right above the "Mark As Read" button. However (and you just knew there were going to be caveats
![[wink2]](http://www.dsboards.com/SMF/Smileys/classic/wink2.gif "Wink #2")
), all unread posts that might have been missed because someone was on the forum but just didn't read them before leaving will only show that way 1) if someone hasn't clicked on any of the "Mark As Read" buttons - and especially the one on the BoardIndex, and 2) someone hasn't already opened a topic to read a post made at a time later than one they might have missed while still being on the forum but not reading it. (I swear I couldn't explain that any simpler. And an example of the latter would be this situation: someone comes to forum, reads a post in a topic made at 11am, stays on the forum while two additional posts, one at 11:30 and one at 11:45, are made to that same topic, doesn't read those latter two, leaves the forum at 12, returns at 1, uses the "Show unread posts since last visit" and reads a post made to that same topic at 12:45 without ever noticing the 11:30 and 11:45 posts. In that situation "All Unread Topics" will not bring up the topic with the two unread/unnoticed posts because the system will consider that since the latest post made at 12:45 has been read, all the posts in that topic have been read unless or until an entirely new post is made to that topic.)
Try clicking on the "All Unread Topics" to see what comes up.
And I realize that all of this may make it sound like it's impossible to catch every post, but that's not actually true. The least complicated way to be sure one catches every post is to visit each board that indicates it has new posts (which is actually what I do). But if someone doesn't want to do that for whatever reason(s) and they prefer to use the "Show unread posts since last visit" feature, yet still hang around the forum afterward while other posts may be being made rather than leaving/logging off immediately, the best thing to do before leaving/logging off is to check the "View the most recent posts on the forum" feature (also located in the "Forum Stats" section of "Dark Shadows Forums - Info Center" on the BoardIndex page) because all of the posts made up to the point someone clicks that link will come up (in reverse chronological order) and they shouldn't ever miss anything. It will also be necessary to click the "Mark As Read" button. However, before doing so be sure to check the "View the most recent posts on the forum" once again to be sure no posts have been made while you were reading those most recent posts.
