I have had this problem for a while, so perhaps there is already a solution out there:

When creating reference dimension to a circle, the default is diameter dimension. Right click it, 'Display as linear'.

But how do you force the linear dimension so that it align with vertical axis? I can drag the (diameter) dimension and 'snap' it to horizontal, and then convert it to linear, but when I try to do the same to vertical, it will snap to vertical axis, but won't give me linear dimension aligned to vertical axis.

FYI, I am using ANSI (the dimension text is always horizontal), SolidWorks 2010 SP2.1.

FYI-2, Under the 'Leaders' tab (dimension property), there is a 'Perpendicular To Axis' button, but I can't do anything to it.

Any suggestion?

Thanks.