A manometer functions as a measurement tool for the pressure of gas. These tools generally measure the pressure of gases that are close to or below atmospheric pressure because atmospheric pressure is used as a gauge for comparison.
Manometers are usually filled with dense liquids, such as mercury or oil, to determine gas pressure. They function by applying the pressure of a gas to the dense fluid on one side while natural atmospheric pressure is applied to the other side. Common designs include a U shape tube with fluid at the bottom, to easily read the difference in pressure on one side. However, other advanced designs include dials and digital faces. Scientists are able to determine gas pressure by comparing the height difference between two columns of fluids.
Since the instrument is dependent on atmospheric pressure, one concern in using a manometer is atmospheric pressure variances. Because this instrument is susceptible to varying pressures, it is impossible to take precise measurements. Due to these variances, scientists often use an average atmospheric pressure amount to reach a reliable result.
The technology used in manometers is used in other instruments, such as barometers. Although these instruments operate based on the same fluid dynamics, barometers are entirely enclosed instruments, designed to measure significant changes in air pressure.