Why are dive tables used?

Dive tables are essential tools used in scuba diving to ensure the safety of divers by helping them determine safe dive times and no-decompression limits. They take into account various factors including the depth of the dive and the duration of exposure to pressure, which are critical in preventing decompression sickness, commonly known as "the bends."

Using dive tables, divers can plan their dives effectively by examining the maximum time they can spend at a specific depth without needing to make a decompression stop during ascent. This planning helps minimize the risk of nitrogen bubbles forming in the body as a result of rapid ascent.

The other choices involve important aspects of diving but are not the primary purpose of dive tables. Calculating air supply needs focuses on the diver's equipment and consumption rather than depth and time, while assessing underwater visibility conditions and deciding on dive gear requirements are considerations that affect dive planning but do not directly relate to the function of dive tables in ensuring diver safety related to time and depth.