About Redefining a Dimension Reference
When you redefine a dimension reference, you can change the reference geometry that you selected for creating an existing dimension. When you redefine the dimension reference, dimension properties, such as tolerances, text format, and so on, are applied to the new dimension.
Select the dimension, and use one of the following methods to redefine the dimension reference:
• Click > 
Attachment.
Attachment.• Right-click and click Edit Attachment on the shortcut menu.
The selected dimension appears grayed out. The Select Reference dialog box opens. The references selection and the preview display are available exactly in the same manner as it is available during the initial dimension placement. When you select a valid new reference, a ghost image of the new dimension with all the properties of the selected dimension appears. The selected dimension is removed when the new dimension is created.
 | The ghost image of the new dimension does not appear if you select an invalid reference. Similarly, if you select an invalid reference for an ordinate dimension, the redefinition of the reference terminates, and the original ordinate dimension is restored. |
You can click Cancel on the Select Reference dialog box to cancel the redefinition process.
When you redefine a dimension reference:
• If you select a circular reference, the ghost image of a radial dimension appears. However, if you double click the circular reference, a diameter dimension is displayed. Additionally, you can right-click and select Diameter or Radius on the shortcut menu as the dimension type. Similarly, for an arc as a reference, you can right-click and select Diameter, Radius, Angular, or Arc Length on the shortcut menu as the dimension type.
• You can select multiple references. The ghost image of the new dimension changes when you select the subsequent references. If you select multiple references, you can right-click and select Double Value on the shortcut menu as the dimension type.
| | You cannot hold down the CTRL key and select multiple references. |
• If you select a point as the first reference, the ghost image for the new dimension does not appear until you select the next point as reference. You can move the pointer to dynamically switch the new dimension type to horizontal, vertical or slanted. Alternatively, you can right-click and select the dimension type as Horizontal, Vertical, Slanted, Parallel To, or Perpendicular To on the shortcut menu.
• If you select an ellipse as a reference, the dimension dynamically switches to the major or minor radii, depending on the location you select on the ellipse. Alternatively, you can right-click and select the dimension type as Minor Radius or Major Radius on the shortcut menu.
• If you select two concentric circles as reference, and select a reference type other than Tangent on the Select Reference dialog box, you can right-click and select the dimension type as Horizontal, Vertical, Parallel To, or Perpendicular To on the shortcut menu. However, if you select Tangent as the reference type, the additional dimension type of Concentric appears on the shortcut menu.
| | You cannot select an arc or its end points as references when you redefine the dimension reference. |