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.
Strain = A change in shape or volume in response to a stress. Stress is the cause, strain is the effect! There are three types of stress: 1) Compressive stress  Forces that squeeze or push toward one another from opposite directions (cause shortening or flattening). 2) Tensional stress  Forces that pull away from one another in opposite directions (cause stretching or extension). 3) Shear stress  Forces that are offset from one another and operate in opposite directions (cause a shear strain). The behavior of rock during stress depends on: 1) The type of rock. 2) The type and amount of stress.