Since crystal lattice plane spacings are accurately known from x-ray measurements, they provide a good test of microscope stability and a calibration of magnification in the upper range of magnification of the instrument.
Plane Spacing 0.9nm and 0.45nm – Asbestos Crocidolite.
The 0.9 nm spacing (020) will be found along the axis of the crocidolite fibers. The 0.45 nm spacing appears at an angle of about 60° in suitable crystal orientations. Because of the hazards of asbestos, this sample is sandwiched between carbon and formvar films, than mounted onto a 3.05 mm grid.