Precision measurement in three-dimensions and mapping require acceptable "standards" for the electron microscope (EM) systems. The best available standards are carbon replicas made from master diffraction gratings. Since these are two-dimensional, certain configurations of convergent micrography can be used to "generate" the third dimension. The process, as has been developped with regard to both Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM), is discussed. The procedure can be used in calibrating any EM system, on-the-job, even on an ad hoc basis. Fundamental to the procedure is the collinearity condition inherent in the imaging system ensuring that the object point, the corresponding image point and the center of projection lie on the same straight line. The consideration of the involved parameters and of the necessary number of micrographs in the solution are discussed. Certain very encouraging results obtained from recent research studies at Laval University are presented.