I'm a fellow diver. I remember the taking off of the mask and putting it back on during training. Came in handy one time because I always dive with my dad and one time we accidentally wore each others masks into the water. Both of us couldn't get the other person's mask adjusted properly to stop leaking so we decided to just switch masks back while under water (we were at 75 feet so didn't wanna go all the way back up). We did it super smoothly so I was very thankful for that training that day or that dive would have been ruined by leaky masks.
RE: SCUBA Diving Basics - Pressure (+ My Bad Experience)