This sketch would be true of either the WF fixture of the luthier tool at 10" from center of dome (neck or tail end) and 5" from center of dome (waist) with the donut or wedge contact point at 1/2" from edge of bit The variance for the shallowest depth (the neck or tail) to the deepest depth (waist) .015" variance. Just the nature of a dome segment in the shape of a guitar
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Of course this variance is dependent on how close the contact point is to the bits cutting edge, radius of the dome and distance variance from the center axis of the dome. But this sketch is pretty close to what we all deal with.