Watch the Size of the Probe to Minimize Uncertainty
(in accordance with Y14.5M-1994 standard)
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.
Tip added September 2002