If there are any leaks in the piping during the calibration, unpredictable errors can occur. Therefore, a leak test should be done prior to calibration. The most simple leak test is to pressurize the system and let the pressure stabilize for some time, and monitor that the pressure does not drop too much. Some calibration systems (pressure controllers) may be able to maintain the pressure even in case of a leak, if it has a continuous controller adjusting the pressure. In that case, it is difficult to see a leak, so the controller should be closed to enable a closed system for a leak test. Adiabatic effect should also always be taken into account in closed system, especially with gas a media, as explained in the next chapter.