Example:
Skibum spends 3 hours on NS / day, and when the red line passes the 3 hour mark, it shows his grade to be approx 63%. Now as his time on NS increases to say, 8 hours, grades drop to approx 23%. This graph assumes that Skibum would get 100% if he spent 0 hours on NS, but due to his inability to read the graph, we can assume he wouldn't get perfect grades, therefore the percentages above would be much lower.
big whoop wanna fight about it?