Change the center point of an object
When you rotate or flip an object in Microsoft Expression Blend, the object moves relative to a fixed point, called the object's center point. When you select an object, the object's center point is marked by a white circle in the object on the artboard. By default, an object's center point is located at the object's center. You can move an object's center point in order to rotate or flip the object around a different point.
Select the object by using the Selection tool.
Do one of the following:
On the artboard, move your pointer over the object's center point icon. When the pointer changes to a four-directional arrow , drag the object's center point to the location that you want.
In the Properties panel, under Transform, do one of the following:
Click the Translate tab. On the Center Point diagram , click the square that you want to be the new center point.
Click the Center Point tab. Change the X, Y, and Z (for three-dimensional objects only) values. You can set numeric values in pixels (or, device-independent units which are approximately 1/96 inch) up to three decimal points for the position.
Double-clicking the center point icon will reset the center point to the default value.