Problem with positioning object relatively to another object I would like to position one object B so its left surface get in contact with the right surface of object A.
I have defined object A with dimension for X: 10 and set it to position (0,0,0) :


I have defined then defined object B with dimension for X: 140 and set to position ((dimension A + dimension B)/2, 0,45), so (75,0,45) :


However as you can see in second screenshot, the respective left and right surfaces are not in line (concerning the X position) (I increased Object B Y position to make the problem more evident).

I also had a look on using some building constraints by specifying that the B left surface should be in the same plan than the A right surface but didn't find it.
I finally found what causes this problem.
The object origin was not right for both objects.
https://docs.blender.org/manual/en/dev/editors/3dview/object/origin.html

For each object : 
Panel:  Tool Shelf ‣ Tools ‣ Edit ‣ Set Origin
Menu:   Object ‣ Transform
Hotkey: Shift-Ctrl-Alt-C
-> Origin to Geometry

However I am still curious if there is a smarter way to specifies that 2 faces should be on the same plan.