The phrase used to quantify the accuracy of a CNC machine is ‘positional accuracy.’ It is calculated by programming the machine to move to a particular value and its deviation from these programmed value is recorded. After taking multiple readings, the statistical average value of the deviations is calculated and this is the positional accuracy of the machine. 0.02mm is the average value for most CNC machines. If your value is not within that range, your machine is most likely not accurate.