To emphasize Rod's tip...
Make sure your cursor shows a CHECK MARK when clicking on the wall and NOT a "mercedes" (surface click)...
By clicking on a surface while dimensioning, you are telling AC to dimension both sides.
Duane
Visual Frontiers
AC25 :|: AC26 :|: AC27
:|: Enscape3.4:|:TwinMotion
DellXPS 4.7ghz i7:|: 8gb GPU 1070ti / Alienware M18 Laptop