Which of the following is done for testing the true running of headstock centre?

• A. Feeler of dial indicator is pressed perpendicular to the taper surface
• B. Feeler of dial indicator is pressed parallel to the taper surface of cent
• C. Feeler of dial indicator is pressed at acute angle to the taper surface of cent
• D. Feeler of dial indicator is pressed at obtuse angle to the taper surface of cent