 The diver descends directly to maximum depth, spends most of the dive at maximum depth and then ascends directly at a safe rate.The sides of the "square" are not truly vertical due to the need for a slow descent to avoid barotrauma and a slow ascent rate to avoid decompression sickness.This type of profile is common for dives at sites where there is a flat sea-bed or where the diver remains at the same place throughout the dive to work.