Atmospheric pressure, which is shown in hectopascal (hPa) or millibar (mBar) or pounds per square inch (psi), changes with differences in altitude?
The various units above are all used to describe atmospheric pressure. There is more information on each unit here:
Atmospheric pressure does change with differences in altitude, decreasing as altitude (distance above sea level) increases. Examples are noticeably thinner air (lower oxygen levels) in mountainous areas compared to locations near sea level. High flying aircraft keep their cabins pressurized to compensate for low air pressure.
It is important to note, when air masses are in vertical motion the rate of pressure change is not a consistent rate.