Using average to find center point for group of vertice

Coding Python Support
1 
    #move entire group of vertices into one central location
    def closeGroup(self,thelist,themesh):

        if(thelist[0]==-1):
            return

        #find mid point of first face
        poly=themesh.data.polygons[thelist[0]]
        newod=(themesh.data.vertices[poly.vertices[0]].co + themesh.data.vertices[poly.vertices[1]].co + themesh.data.vertices[poly.vertices[2]].co )/3

        scan=1
        while(thelist[scan]!= -1):
            poly=themesh.data.polygons[thelist[scan]]

            #first find mid point of face
            newod2=(themesh.data.vertices[poly.vertices[0]].co+themesh.data.vertices[poly.vertices[1]].co+themesh.data.vertices[poly.vertices[2]].co)/3
   
            #find mid point of faces
            newod=(newod+newod2)/2

            scan+=1

        scan=0
        while(thelist[scan]!= -1):
            poly=themesh.data.polygons[thelist[scan]]
            themesh.data.vertices[poly.vertices[0]].co=newod
            themesh.data.vertices[poly.vertices[1]].co=newod
            themesh.data.vertices[poly.vertices[2]].co=newod
            scan+=1

        

        return

The result is off center position. I cannot find out what is wrong with it.

2

What value are you expecting, and what value are you getting? Nailing that down will probably help you find the error in your math

3

Use the vertex locations to calculate the central point.