This video shows how to change the orientation of a diameter dimension. To get a perfect horizontal or vertical, a snap may be used.
You can also do this using the drawing properties. Open the drawing properties and just check the “show as linear dimension” in and click ok. (See image on left side).
To do this in Pro E 5.0 and Creo, go to drawing properties and under display tab, expand configuration and click linear.
The “Text orientation” just below show as linear dimension option is used to get different orientation only when it is not linear.