Final answer:
A portable vacuum gauge is used to measure the negative pressure inside a vacuum chamber or system.
Step-by-step explanation:
A portable vacuum gauge is used to check the pressure of a vacuum. It is specifically designed to measure the negative pressure inside a vacuum chamber or system. The gauge provides a reading that indicates how much lower the pressure is compared to atmospheric pressure. For example, in many physics experiments conducted in a vacuum chamber, the pressure gauge on the chamber will read a negative value to indicate the reduced pressure inside.