I don't understand the first test. It seems to measure bed flatness, it does not depend on the column being vertical to the bed.

The rotating DTI is good, but you want to do North South, East and West to get a vertical.

To compare sensitive quill movement to Z slide movement is trickier. How about putting a bar in a collet, putting your DTI against it from the side and from the front, then comparing quill movement to slide movement. How's that?