Boyle's law, also referred to as the Boyle–Mariotte law, or Mariotte's law, is an experimental gas law that describes how the pressure of a gas tends to increase as the volume of the container decreases.

Does this sound like boring stuff from school? :-(

Yes, it does as well for me. Nevertheless an in-depth understanding of Boyle-Mariotte Law is essential for a freediving or SCUBA student. If you are a diving instructor, tell your students to download the app and "play around" with it. You will notice that they will understand the physics without much theory in the class room.