There are a few simple formulas that can be utilized to calculate PFD. The proof test coverage is not taken into consideration. It is considered that the procedure used for the test is in every way accurate.
In the more advanced version, the calculation takes into consideration the proof test coverage.
During the study, it is necessary to take into consideration the anticipated lifespan or mission time of the components that have been chosen. The computation is based on the procedures that are outlined in the VDI/VDE 2180 (part 3) and the IEC-61508-6.