Before the diveTake the lanyard off your wrist and put it on theirs.Ask them what their plan is for the dive.Use their answer to calculate how long their dive should take.If requested, adjust the line to their desired depth.
During the diveTime the dive, either with a watch or by counting "one thousand, two thousand..." in your head.Feel the dive by putting your hand on the line in a shaka shape and pressing with your thumb to feel the vibrations of the lanyard on the line.