I wouldn't overly concern yourself with the formula as it is confusing, but basically it's saying you can only get 14 activity points every two weeks and to get those you need to make the 14 posts. However, you only need to make one post in each activity period to get the potential merit? and you can collect the rest later by making the required posts. Everything is explained here: https://bitcointalk.org/index.php?topic=2766177.0