Abstract: Apparatus for changing the stitch length of double lock stitch sewing machine while the machine is in operation. The apparatus including a first transmission having a variable transmission ratio that can be connected to the machine needle rocking assembly, and a second transmission having a variable transmission ration that can be connected to the machine feed dog assembly. Additionally, the apparatus includes an actuator connected to the first and second transmission that may be activated by a machine operator for synchronously changing the transmission ratio of the first and second transmission to effect change in the machine stitch.