On Thu, 28 Jan 2010 22:06:52 -0600, Ignoramus2532
wrote:

In other words, the indicator does not really tell me if the carriage
moves parallel to the imaginary axis of the spindle rotation, because
that axis was not used in any way

Use RDM (Rollie's Dad's Method). Dead simple, and even eliminates
errors in the test bar. The only requirement is that the test bar is
round at the measurement points.
--
RoRo