 With dive tables, it is generally assumed that the dive profile is a "square dive", meaning that the diver descends to maximum depth immediately and stays at the same depth until resurfacing (approximating a rectangular outline when drawn in a coordinate system where one axis is depth and the other is duration).Some dive tables also assume physical condition or acceptance of a specific level of risk from the diver.Some recreational tables only provide for no-stop dives at sea level sites, but the more complete tables can take into account staged decompression dives and dives performed at altitude.