Manometer

A manometer is a device that is able to measure the pressure of a medium (a liquid, or a gas), it also uses to check the pressure of cylinder but it can only check the inner pressure not outer.In most cases, the relative pressure will be measured. A barometer can measure the absolute pressure, compared to a vacuum. There are different designs, for different applications.
The name ("manometer") comes from Ancient Greek, μανός manós -thin and μέτρον métron measurement, or ruler.
Many animals have a tympanic membrane (or eardrum), which only reacts to changes in pressure.