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The Y14.5 Standard states that
surface controls such as profile of a surface and parallelism
control all points within the surface. It is never possible to
inspect all points within a surface. Inspection always comes
down to work vs. risk. If the inspector wants to reduce the
risk of accepting out of spec parts, the uncertainty of the
measurement needs to be considered. Mil Standard 120 and many
corporate standards require that the uncertainty be included
within the allowable limits. There are many sources of
uncertainty. One that is often overlooked is the surface
roughness that is mechanically filtered out by the contacting
probe. The larger the radius of the probe, the greater the
amount of surface roughness that will be missed and the
greater the uncertainty of measurement.
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