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The JCM's are morphs which adjust or compensate for the deformation applied by Poser's joints.

The .cr2 listings for twist and joint contain the settings for the falloff spheres and bend angles or twist deformers of the joint.

There's probably no need to be concerned with any of this when making JCM's, unless you want to adjust Antonia's joint setup.

Cage, thank you!  I made progress on my conforming clothing for Antonia.  I noticed that your conforming shorts is using a mesh similar to Antonia, mine is not.  Is there any mathematical method to calculate the deltas for the JCM?  Doing it by trial-and-error takes a lot of time.