We generally wait until the bubbles stop coming up then have the line tender reel the diver in. 
Just kidding. We use line signals with the boat crew tracking the down time and watching the bubbles to judge consumption. Also the diver is responsible for monitoring his own consumption and surfacing to check whenever he feels the need.

Just kidding. We use line signals with the boat crew tracking the down time and watching the bubbles to judge consumption. Also the diver is responsible for monitoring his own consumption and surfacing to check whenever he feels the need.