In this experiment a sample of a gas (air) is in the syringe. The syringe is connected by a plastic tube to a pressure transducer. The transducer measures the pressure exerted by the gas in the syringe in lb in^-2.

When the volume of air in the syringe is decreased by pushing on the plunger we can see what happens to the pressure...it goes up.

When the volume of air in the syringe is increased by pulling on the plunger we can see what happens to the pressure...it goes down.

This demonstrates the relationship between pressure and volume for a gas. As the volume decreases the pressure increases. This is an inverse relationship.