If the measured feature and the datum feature are parallel to one another, then measure the displacement and compare it to the basic. Chart the point to establish process control. When control is established, determine the size of the profile zone required to contain each measured point and compare the mean and associated standard deviation of the resultant zones to specified profile tolerance. Report Cpk from (Cpu or Cpku) in other words compare the encroachment of the distribution on the upper limit and discard the Cpl.
If Datum A is an axis and the measured feature is displaced from it then the measured points can be compared from their basics, charted and controlled, reported according to the size of the zone necessary to contain each one, and predicted for capability. Just like above.
If the measured feature is defined at any other angle than 180 degrees to the datum feature plane or axis then only orientation to A can be determined. For instance a surface or axis can be measured for perpendicularity to a datum surface or axis. Note: The measured feature is free to rotate perpendicular to the datum surface A. Chart the oriented feature form deviation which is the size of the profile zone needed to contain all measured points on the feature. Establish control and then use the same resultant zones to predict capability.
If the datum feature A is a point (center of a sphere) then the displacement can be measured as well but it is probably easier to orient the measured feature and measure the displacement of the datum feature to it.
Good luck, Paul
