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The formula Sin B = b/a is used in order to calculate the required height of the gauge blocks needed for measurement. In this formula, B is the required angle, b is the height of triangle, and a is the length of hypotenuse. As an example, let’s say we want to take a measurement of the straightness of a part surface that has a 27° angle from another reference surface on the same part, and we are using a sine bar or sine plate that has 5 inches between the two cylinder centers. Using a qualified calculator, we complete the formula Sin 27° = b/5″ giving us the answer b = 2.270″. Then we know the needed height of the gauge blocks to place under the upper cylinder of the sine bar or sine plate that makes the part surface 27° out-of-parallel with the surface plate. Then, the part surface will be parallel to the surface plate when placed facing the opposite direction and on top of the sine bar or sine plate. From here, we are able to measure the part for straightness, flatness, the accuracy of the angles, or any other number of potential measurements.

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