How do the gas laws operate in scuba diving? I mean to exclude the rule of never holding your breath...

The golden rule of scuba is NEVER to hold your breath. Why not? Because if you got a lung-full of air, and you ascend without exhaling, the difference in pressure, caused by the difference in mass of the water above you at various depths, may cause your lungs to explode. I know you excluded this scenario in your question, but it is one your instructor will emphasize, and he should do so, because a lot of recreational divers have perished this way.

As to the Ideal Gas law, the more you fill your tank when refilling, means the more mass of air in your container....most of us can readily pick up a full tank...and differentiate the full tank from the empty tank just by mass.

I will try to think of some more...

The gas laws, particularly Boyle's law and Henry's law, are crucial in scuba diving to understand how gases behave under pressure and affect divers' bodies. Boyle's law states that the pressure of a gas is inversely proportional to its volume when the temperature remains constant. This law is relevant in scuba diving because as a diver descends underwater, the pressure increases, causing the volume of air in the diver's lungs and equipment to decrease. Understanding Boyle's law helps divers manage their buoyancy and avoid lung overexpansion injuries.

Henry's law, on the other hand, describes how the concentration of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. In scuba diving, this means that as a diver descends and the pressure increases, more gas (such as nitrogen and oxygen) is absorbed into the bloodstream. Ascending too quickly can lead to decompression sickness, as the dissolved gases may form bubbles in the body tissues.

Overall, adherence to gas laws is essential for safe scuba diving, as it helps divers manage gas pressures in their equipment and understand how gases interact with their bodies at different depths.