Shadow cast carbon replicas of diffraction line gratings (spacing 462.9 nm) which are used typically for calibrating electron-optical magnifications up to the x80,000 to x100,000 range.
Rulings of 2160 lines/mm, ruled at 90° to one another, give additional accuracy to magnification checks and aid in checking distortion. These replicas should be used with care, avoiding excessive exposure at high probe/beam currents.