“Biff’s right. A good rule to follow is not to rise to the surface any faster than the escaping air bubbles. Your body has to adjust to the variations in water pressure. All right, let’s go out and try it in the water now.”
They climbed in the dory. Uncle Charlie started the outboard, and they moved offshore about fifty feet.
“Sound for depth, Biff.”
Biff dropped a sounding line overboard. He pulled it up, examined the leads marking off every three feet.
“Thirty feet, Uncle Charlie.”
“Okay. Now you know how to clear your masks.”
Both boys nodded their heads.
“I want to hear you tell me.”
Biff began promptly: “If water seeps into your mask, clouding the glass and obscuring your vision, you roll over on your back—”
“Take it from there, Derek,” Charlie cut in.