About Moving a Linear or Angular Dimension
When you move a linear dimension within the zone, it automatically snaps to the midpoint of the witness lines.
When you move an angular dimension, it automatically snaps to the center of the angle being dimensioned. If you move the dimension to the opposite side of the angle, it snaps to the center of the angle, on the opposite side.
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Snapping occurs for both driving and driven dimensions, except for clipped dimensions.