The oil-filled Bourdon tube depth gauge operates on the principle of pressure affecting a sealed coiled tube, which is why it is identified as the correct answer. When submerged, water pressure increases, and this pressure acts on the fluid inside the Bourdon tube, causing the tube to coil tighter. As the pressure increases, the curvature of the coiled tube changes. This movement is then translated into a reading that indicates the depth of the dive.
The Bourdon tube mechanism is effective because the oil inside helps to dampen any rapid movements and provides a smoother reading by compensating for any sudden pressures. This design ensures that divers have reliable information about their depth, vital for safety and navigation underwater.
While diaphragm and electronic gauges are other types used in scuba diving, they operate on different principles. Diaphragm gauges use a flexible diaphragm that deflects under pressure, and electronic gauges use pressure sensors to provide readings. Both serve the purpose of measuring depth but do not utilize the coiled tube principle central to the operation of oil-filled Bourdon tubes.