Quality Digest

We centerless grind long, 20 - 24', round 1"-12" steel bars.When it comes to measuring straightness,in thousandths of an inch, and/or out of round, also in thousandths, we sometimes run into debates because we, our competitors and customers don't always utilize the same methodology. Beacuse of the size and weight of the bars, they generally have to be measured "in place", typically while resting on V-blocks.
What do you recommend as an optimum method of measuring straightness, e.g. for .002"/foot TIR, or out of roundness,e.g. on a 6" round bar ? We believe that some of our customers are measuring "out of straight" when attempting to measure out of round, ( based upon where/how they support the bar and place their dial indicator), or vice versa due to the methods employed. How would you approach this ?
The largest three point micrometer that I'm aware of, measures up through 2" round. Is there a particular reason that three point micrometers haven't been developed to measure roundness for larger rounds ?
Thank You for your help.