Dimensions lines do not snap to guide lines the way you are wishing them to, in order to establish an offset for your dimension lines. 

But once you set the offset of your first dimension the rest of the dimensions in line with it should snap to the same offset. Maybe you could describe what problem you are having in more detail. As long as you keep the axis inference the same they snap into line easily.

You can adjust the offset with the move tool if you want to modify it after you create it. 

David

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