It is very important to test circular motion accuracy of NC machine tools as it affects all other machines machined by them in industries. In this paper, it has become possible to detect errors of linear displacement of radial directions for circle tar motion accuracy test using newly assembled magnetic type of linear scale so called Magnescale ball-bar system. It has also organized computer program systems using tick pulses come out from computer for getting error motion data at colt start time interval in circular motion test on NC lathe. Error data gotten from test is expressed to plots and analysed to numerics by various statistical treatments.