My friend and I are on a boat dive in British Columbia.  On the the first dive of the day, we are both diving 100 cubic feet (cf) tanks.  Mine is a high pressure steel rated at 3500 psi.  My buddies is a low pressure steel tank rated at 2400 psi, both 100cf.  At the end of the first dive, we both have 500 psi left.  Who has more air? Or are they equal?  Think about it.  Answer next week.  Correct answer is the low pressure steel has more air.