What is the equation for converting depth to ATA?

The equation for converting depth to absolute pressure in atmospheres (ATA) is based on the understanding that one atmosphere of pressure is present at sea level, which is equivalent to a depth of 33 feet in water. The formula used to calculate the ATA at a given depth is:

[ \text{ATA} = \frac{(D + 33)}{33} ]

Where (D) represents the depth in feet. This equation adds an additional atmosphere from the surface air pressure (the 33 feet) to the depth pressure, because as a diver descends, the pressure increases for every 33 feet of sea water.

At the surface, which is 0 feet deep, the pressure is 1 ATA (the atmospheric pressure). For any depth (D), the total pressure can be found by recognizing that there is 1 ATA from the air above the surface, and as the depth increases, pressure from the water column adds additional pressure relative to the surface.

Consequently, the formula correctly accounts for the contributions of both the atmospheric pressure and the water column pressure to yield the total pressure in atmospheres.