How are surface profiles calculated when using patch compounds?

[[Ja...]]

I've screenshotted an image showing the upper and lower areas on my surface, but they don't appear to link to my Actual? What is driving the Actual result?

[[Na...]]

Hello Jack,

for the surface profile virtual spheres are placed on the nominal surface, with their center point on the nominal surface. The deviation of +0.78 is the distance from the actual data to the nominal at this spot. A GD&T check returns the "worst" result - in this case you would need a sphere with a diameter of 1.57 to find the actual data inside the tolerance zone (1.57 ~= 2*0.78, should be clearer with more digits). There are some pictures in the direct help for the surface profile to illustrate this.

Regards,

Nanno