Ear equalization training tool, practicing ear pressure balance for freediving/diving spearfishing underwater. Make of alloys, strong, stable, and long terms use. Light in weight and compacts in size, easy to carry and store. Suitable for most beginner and professional diver, and underwater sports, scubas diving or diving. The double side middle grooves design is more ergonomic, improves grip strength, and makes handheld use more stable.