As you create or select geometry, Revit displays temporary dimensions around the component. This is useful for placing the component in the proper place.
Temporary dimensions are created to the nearest perpendicular component and increment by the set value. For example, if you set the snap to 6 cm, the dimension increments in values of 6 cm as you move the component to place it. For information on changing the dimension snap value, see Setting Snap Increments.
After you place a component, Revit displays the temporary dimensions. When you place another component, the temporary dimensions for the previous component no longer display. To view the temporary dimensions of a component, click Modify and select the component. Remember, the temporary dimensions are to the nearest component, so the dimensions you see may be different from the original temporary dimensions. If there are dimensions you want displayed at all times, create permanent dimensions.
You can modify temporary dimensions to reference the components you want by moving the witness lines. You can also specify the display and placement of temporary dimensions.