i have a question reagarding the linear periodic symmetry. I want to model an infinite array of blocks like in the picture. 

I am not sure about the right settings for the symmetry. As low and high boundary i choosed the three faces on each side (you can see the blue faces in the picture). The direction of periodicity is the x - axis, but what is meant with linear shift? No matter what i choose - i will get an error message with a failed meshing.

Thanks for your help!


Beste regards,