The concept of the turnaround point in technical diving and how it is calculated precisely to guarantee a safe return.
The turnaround point is a decision that saves life in technical diving and cave diving.
The point at which you must start returning before air runs out. It is calculated by dividing air into three thirds: one third to go, one third to return, and one third for emergencies.
The return is always harder than going out. Fatigue and emergencies consume more air than you expect.
The diver who calculates their turnaround point precisely is not surprised by running out of air.