Abstract: The present invention is directed to a positioning apparatus which is used to position work pieces in a work piece securing mechanism during a computer controlled machining operation. The apparatus includes an arm which is slidably mounted on a graduated shaft so that the position of the arm from a zero reference point can be determined. The apparatus may also include a second graduated shaft slidably mounted in the arm so that the position of a work piece inside a work piece securing mechanism can be determined in relation to a zero reference point. The apparatus of this invention can repeatedly position work pieces within about 0.0005 inch (0.0013 cm) of a desired position, or better.