In order to measure the errors of a five-axis machine tool quickly and accurately, the R-test was developed. In this paper, the current research status of the R-test device worldwide and presents its typical working principle and structure were introduced and the idealistic and realistic error model of this measurement device were constructed. Besides, the transformation matrix from sensor readings and precision ball center dimensions were established, and effect of all error sources on the accuracy of the error measurement device was displayed according to sensitivity analysis. Finally, the error measurement accuracy of this error measurement device was analyzed by Monte-Carlo analysis.