thanks all for the reply
the thick,
the centroid that i need , is the centroid from a sketch.
the sketch (symetric)is driven and have no features.
with the section properties i can see the centroid.
what i did, is calculate the Y-position and link a formula with the equitation to the dimension:
Y = ((y1*area1)+(y2*area2))/(area1+area2)