Using the moiré technique or the related geometrical phase technique [1,2], lattice displacement fields can be derived from high resolution micrographs by comparison with an undistorted reference lattice. A moiré image gives a magnified view of the distortions in a high resolution image, whether they are due to a distortion of the crystal lattice or result from imaging artifacts. The magnification of a moiré image is determined by the choice of the reference lattice. The closer the reference lattice is to the average lattice period in a high resolution image, the larger the magnification. To first order, both rotations and extensions of the lattice are magnified by the same factor g/Δg, where Δg is the difference between the image lattice and the reference lattice . When the moiré technique is applied to interfaces, care must be taken interpret only patterns from corresponding sets of lattice planes. Thus, the technique gives a good representation of the distortions around a precipitate, but the interpretation of the moiré pattern inside a precipitate or across an interface must be made with caution.