Exact magnification depends first on the adjustments made on installing an electron microscope. It must be controlled later by means of test specimens (e.g., beef liver catalase crystals 13 or T4 phage tails) because magnification may change over time and at every repair. Latex crystals and diffraction grating replicas are for low magnification only and to be rejected. In "manual" TEMs, magnification is easily and rapidly adjusted in the darkroom by means of a photographical enlarger. In "digital" TEMs, magnification can be controlled, if necessary, by calculation of correction factors. This potentially tedious procedure seems to be very unpopular with today's phage electron microscopists. Indeed, magnification control is seldom mentioned in recent phage descriptions and one suspects that it is rarely done. As a result, particle dimensions from "digital" TEMs sometimes appear as products of fantasy.