formed gratings. In the last case sensitivity is limited hy the requirement for photographing the deformed grating lines. Images of gratings denser than about 40 lpmm are difficult to resolve with current optical systems. For a typical shift of Ii mm, assuming precision to lfLoth of a fringe, Ii X 10-4 can therefore he achieved. A variety of optical processing methods can also be employed such as the spatial filtering of crossed, superposed gratings to completely determine all components of the in-plane strain tensor as illustrated in Fig. 1. It is not clear to the discussors whether similar optical processing methods can be applied to the holographic methods.