My wife did not want to dive the Blue Hole in Belize so I decided I would keep a close eye on a diver that had just got certified 4 days before. We got down to about 120' when he started messing with his camera, he was vertical and steadily finning but still sinking, I swam over in front of him got his attention and gave him the signal to add air to his BC. Instead of adding air to his BC he thought I wanted him to take my picture, gave him the signal again and he took my picture again as we are slowly sinking, so I swam over grabbed his inflator held on to him and added air, he was a little offended that I had done that but was totally unaware that we had ended up at 141' till we were back on the boat. Our guide thanked me several times and again as we were heading home a few days later. This could have had a lot different outcome if I had not had so much practice herding students during OW classes.
