Mid-point
3-D Standard > HCM > Coinc.. 
> Mid-point 
Use this function to determine a point as a mid-point between 2 graphical elements.
Proceed as follows:
First, identify as Geometries the mid-point to be fixed and then the two geometry elements that are to serve as reference points.
The other control elements are described in the topic Dimensional and Positional Constraints.
