Time to change refill / Refills

While taking notes in class or a meeting, you may encounter this problem. The gel ink pen refill will run out before you notice it. And you may miss the key point after finding a new refill to use.
“Time to change refill” is to add a kind of impurity into a small part of printing ink where lies in the front of end. When the ink is soon used up, you will notice it by writing the words with impurity. Then you can prepare another refill during break time.