If the screen width is 7 feet and the projector's throw ratio is 2.0 - 2.4:1 (because projectors have zoom lenses, they also have a range of throw ratios) then you can place your projector anywhere from 14 to 16.8 feet away from the screen.
A strain gauge (or strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern.he gauge is far more sensitive to strain in the vertical direction than in the horizontal direction.
Definitions of stress and strain. Nominal stress: the force on the object divided by the original area. True stress: the force on the object divided by the actual area. E.g., when necking occurs the true stress is the force applied divided by the area of the neck. The unit for stress is Nm-2, or Pa. Nominal strain: change in dimension / original dimension. This is also known as the engineering strain, and is strictly only true for very small displacements.