A horizontal constraint parameter controls the X distance between two points on one object, or between two objects.
linear dimension represents the distance between two points, a horizontal constraint parameter defines and controls the horizontal distance between two points.
While aIn the example below, the polygon on the left has a horizontal constraint of 1 unit applied to the top line of the polygon. When that polygon is rotated, the result is the polygon on the right. The constrained points will remain 1 unit apart horizontally.