FIDUCIAL
Refers to the physical marking of a sample mount with a number of reference marks, so that all data can be referenced directly to those marks on the sample surface. This is used to provide a method of re-locating specific positions even after the sample has been removed from the sample holder. This method can also be used to relocate coordinates from an entirely different coordinate system such as a digitizing microscope stage. In the Probe for EPMA software package all samples using this feature must have 3 fiducial marks. This is because the program assumes that the positions are digitized in three dimensions (fixed to x, y and x).