It is very important to maintain equal pressure in your air spaces to the surrounding pressure. This is known as equalization and involves adding air to these spaces as you descend. You will most likely already have experienced these changes in pressure at some point in your life—whether going over a mountain, traveling in a plane or being at the bottom of a swimming pool. Small changes in pressure may be managed by simply swallowing or wriggling the jaw. You will typically hear a pop or crackling sensation in your ears when the pressure equalizes. During a scuba dive, pressure changes rapidly. The fastest change is in the first few meters or feet. Therefore, it is very important to equalize early, often, and approximately every 1 meter/3 feet on the way down.