The countdown exercise was, so far, only mentioned in Book 8: Legacy, when Councillor Oralie was trying to get Sophie to control her enhancing ability. It is normally used in Empathy training.
Sophie's Countdown Exercise
When Sophie did the countdown exercise, she had to do it differently, due to her many abilities. She thought of five words to describe how it feels when she uses her telepathy (unifying, draining, energizing, inspiring, and frightening), four words to describe her inflicting ability (overwhelming, empowering, unsettling, and refreshing), three words to describe her teleporting (liberating, surprising, and alarming), two words to describe her Polygot ability (humbling, and uplifting), and one word to describe her enhancing ability (restricting). After she said that enhancing made her feel restricted, her enchancing was turned off. When she wanted it to turn on again, it turned on.
Empathy Countdown Exercise
Empathy have to use the countdown exercise to separate their own emotions for, the ones that they are reading. They have to learn not to judge, condemn or interfere with either if the feelings.