Profile of a Surface with No Datums

In this Question Line video, Jason answers the following submitted question regarding profile of a surface with no datums referenced in the feature control frame: 

I have a form only “profile of a surface,” it has no call out to a datum on the drawing. Without a datum, should my CMM measurement for Max and Min be the same deviation from the target, or is it normal to varying deviation from the target (positive or negative bias). My thinking is that the CMM should be working on “best fit” and centering the measured profile vs the nominal profile. 

Jason walks through a few examples to show the difference between profile of surface with and without datums referenced in the feature control frame.  With datum features referenced, form, location, and orientation of the surface are all being controlled. Removing the datum feature references results in only form being controlled. Jason explains how both of these scenarios affect the reported deviation of the surface. 

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