Most of us use google reader to track various website feeds and updates, but when it comes to reading feeds we end missing reading so many feeds on a day to day basis which results in so many unread items in google reader. However there is Mark All As Read button google reader which allows you to mark all as read in two mouse clicks.
One of my friend asked me, how can he just undo the mark all as read in google reader and yes google reader allows you to mark all as read. Here is how you can do it.
1. Open google reader at google.com/reader and login with your username and password
2. Now, under any subscriptions tags which you click to read in the left pane.
3. You will see the button Mark all as read at the top left of the reading pane in google reader.
4. Click the arrow on the right of the Mark all as read button and then select Items older than a day, Items older than a week or Items older than two weeks
5. This way you can undo mark all as read step by step, and decrease the number of unread items.