In single needle lockstitch sewing machines, the needle thread consumption of 10 normal stitches for a fabric with a particular number of layers at a particular stitches per unit length is manually measured kept as a reference value. If the value of needle thread consumed per stitch is very small, the length of thread consumed per 10 stitches is used as a comparing value. The actual thread consumed for every 10 stitches is measured online by a rotary optical encoder sensor by converting the angular movement into the linear movement of the thread and continually compared with the reference value. If the online measured length is more or less a buzzer sounds to indicate the variation. The counting of every stitch formed is undertaken by a proximity sensor by sensing the protrusion in the hand wheel of the machine, which rotates once for every rotation.