Stress testing of films: Like stretching a piece of plastic wrap over a plate films deposited on substrates can have stress which makes them taunt. This is an example of what is called tensile stress. If the plate is a paper plate rather than a ceramic plate this stress can cause it to warp, curling up in the tensile case, and this warping can be measured using a stress tester. The Flexus 2320 stress tester at SNF reflects light at an angle as multiple positions across the surface onto a detector, if this surface is not flat but instead curved a bit like a bowl the reflected spot will in higher position than expected as the light is reflected along spots away from the center. The position of the spot along with knowledge of the film and plate's mechanical properties allow the film stress to be calculated. Unlike plastic wrap on a paper plate films can also be cause the plate to bend in the oppsite direction, the stress that creates this type of bending is called compressive stress.