The effect of the reading errors and the angular misalignments of the probes on the accuracy for roundness measurement with three point method has been analyzed in detail in this paper.Based on the principle of three point method and error analysis theory

the error propagation equations of the reading errors and the angular misalignments of the probes in roundness measurement are derived.It is found that the root cause for the distortion of the roundness measured by three point method is the improper arrangement of the three probes' angular position which makes the reading errors over amplified at some harmonics of roundness.In order to improve the accuracy for roundness measurement by three point method

the angles between three probes must be optimized so that the effect of the reading errors and the angular misalignments on the accuracy for the measurements of all harmonics of roudness could be minimized.