Abstract: A computer aided error measurement system is disclosed. The horizontal and vertical straightness errors as well as roll, pitch and yaw errors are measured simultaneously with just one setup according to the system. The system includes a computer and related components thereof. The system also includes a light source, two beam splitters, and three photodetectors. The output signals are inputted into the computer via amplifying circuits and an analog to digital converter. The computer actuates a motor driver to drive a stepping motor and controls a feed axis with the motion errors. The whole measurement takes are performed in very short time and in real time.