User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-7594114-20130402145059/@comment-1515612-20130403002500

Okay for once and for all.

The Lightning Theif - 12 turning 13.

The Sea of Monsters - 13 turning 14.

The Titan's Curse - Still 14.

The Battle of the Labyrinth - 14 turning 15.

The Last Olympian - 15 turning 16.