When measuring the absolute pressure with absolute pressure transmitters, a perfect vacuum is assumed as a reference value. This type of pressure reference is the relative pressure of the medium and the pressure of the atmosphere. If the location changes during absolute pressure measurement, especially if there is a major change in altitude, the reference value may change due to the change in atmospheric pressure. When using an absolute pressure transmitter, the reference of a changing atmospheric pressure is not necessary, because one relies on certain pressure ranges of the absolute pressure transmitter.

Relative pressure uses the atmosphere (medium air) around the sensor as a reference. To measure exactly what kind of pressure is prevailing, a reference pressure value is required because the sensor element of the relative pressure transmitter shows a deflection due to pressure changes. One of the main reasons for using relative pressure transmitters to measure relative pressure is to ensure that anywhere in the world, a reference to the location where the transmitters are installed.