Dive time is limited due to the limited capacity of the tank.
For safety, if you leave the tank residual pressure at 50 atm and exit, the practical dive time can be roughly calculated by the following formula.
The unit of volume is liter and the unit of pressure is atm pressure.

1．Maximum water depth ÷ 10 + 1 = Maximum water depth pressure

2．Tank volume x (Start pressure-50) ÷ Air consumption ratio ÷ Pressure at maximum water depth = Practical dive time

◆◇◆ Question ◆◇◆

A diver with an air consumption ratio of 30 liters / min dives to a depth of 20m.
If you equip a 12 liter tank filled with 200 atm and leave the remaining pressure of the tank at 50 atm, then how many minutes is the practical dive time?

◆◇◆ Answer ◆◇◆

Tank volume is 12 liters.
Start pressure is 200 atm.
Maximum water depth is 20m.
Calculating with the above formula, the practical dive time is about 19 minutes as below.

1．20m (Maximum water depth)÷ 10 + 1 = 3 atm (Maximum water depth pressure)
2．12 liters（Tank volume） ×（200 atm（Start pressure）－50 atm）÷30 iters / min（Air consumption ratio）÷3 atm（Pressure at maximum water depth）＝19.9 minutes（Practical dive time）