An altitude dive is any dive made above _____ feet/meters requiring the use of special conversion tables.

An altitude dive refers to any dive that takes place at a height above a certain elevation, specifically indicated by a threshold that necessitates the use of special tables for calculating nitrogen absorption and decompression requirements. The correct answer indicates that an altitude dive is classified as any dive made above 999 feet or 304 meters. This threshold is important because at elevations above this level, the partial pressure of gases changes, which impacts dive physiology, particularly with regard to decompression sickness risk and nitrogen narcosis.

At elevations above 999 feet/304 meters, divers must consider these changes and adjust their diving plans accordingly, using specialized conversion tables designed for such conditions. This ensures that divers have the necessary information to manage their ascent and descent safely while mitigating the risks associated with altitude diving.

The other options presented do not accurately represent the threshold for altitude diving, either being too low or misaligned with the scientific standards established for diving at high altitudes.