Set a Coordinate System in Vision Assistant has wrong x-axis angle

I use Vision Assistant 2019, 32 bit.

When I have 2 points from Find Circular Edge, I use Caliper: Line Fit, to make a line from that 2 points.

And then Set Coordinate System, using angular motion mode, which the only X-axis angle that I can refer to is the line from Line Fit.

Finally I saw that the X-axis angle is not related to the line that I refer to.
Is there any explanation? 

Or is there other method that I can set the x-axis correctly to the line?

Thanks.