Pressure calibration is as important today as it has been for a very long time, but the way calibration is done and the equipment used to do it has changed drastically. In the past it was a standard practice to use a primary standard for pressure calibration. That standard was normally a dead weight tester or a manometer. Today with more accurate secondary standards available there is a larger choice in what can be used for pressure calibration. What is used normally will depend on the requirements that have to be met and the equipment that is available