If a Bourdon tube pressure gauge is submerged to a depth of 200 feet, what will it read?

A Bourdon tube pressure gauge measures the pressure of a fluid acting on its inlet. When submerged in water, the pressure applied inside the gauge will equal the pressure applied outside due to the water's depth. At 200 feet underwater, the water exerts pressure based on its depth, but since the gauge is designed to measure gauge pressure (which disregards atmospheric pressure), it will show 0 pressure when fully submerged. This is because the pressure inside the Bourdon tube equalizes with the water pressure outside.

In this context, the gauge does not read the surrounding water pressure, as it is calibrated to zero at atmospheric pressure. Therefore, when submerged, the gauge reflects the fact that the pressures are balanced, leading to a reading of 0. Understanding how the water pressure interacts with the gauge's internal pressure allows us to see why the reading is at zero when fully submerged.