This chapter presents a method of calibration for scanning electron microscopes (SEMs). The described calibration method is a twofold step. The first step evaluates the dynamical drift parameters. The second step estimates the parameters of the geometric projection and the static distortion. Both steps process the calibration parameters across the range of magnification scales, thanks to a representation with partial differential equations. The chapter is provided with an example of calibration of the JEOL JSM 820 and an example of application in metrology. The presented method is not the unique way of calibrating an SEM and can be a good start to inspire other methods of calibration.