the machine the number of stitches from the starting point are counted by the encoder within drive unit 42 the reflective tape 54 will be covered by the material and the beams of the sensors 40 are blocked by the material when the edge of the material moves past the reflective tape 54 the sensor beams are reflected from the reflective tape 54 and sensed this provides the system with an indication of the location of the edge of the material so that the seam length can be stopped at a given distance from the material edge the system is originally taught by the operator to sew a given number of whole and partial stitches x in a seam after the edge of the material is detected and will then sew x stitches before terminating the seam depending upon the percentage of the stitch which has been sewn at the time of detection of the material edge the reverse sew mechanism is positioned to vary the length of the last stitch sewn to provide increased accuracy to the seam termination referring to fig4 an enlarged view of the reverse sew assembly is illustrated a stepper motor 21 is actuated to pivot reverse sew mechanism 17 about a pivot point 23 mechanism 17 is illustrated in the solid line position in its normal operating position in the forward sew mode when the stepper motor 21 is actuated mechanism 17 is pivoted about pivot point 23 to reduce the length of the last stitch in the seam it will be understood too that other techniques may be used to vary the length of the last stitch for example the material feeding mechanism known as feed dogs may be retracted by an air cylinder while the last stitch is being formed the.