for the control circuit 103 the slot switch 89 acting as path dependent switch is connected with the relay 100 which upon release of slot switch 89 switches the make and break contact 99 in such a way that the potentiometer 97 which serves to set the tension stitch length l sp is connected with the dividing element 101 the slot switch 90 which also acts as path dependent switch is connected with relay 95 which upon release of the slot switch 90 switches contact 94 to open position thus interrupting the circuit of the sewing machine motor 92 the stitch group sewing machine operates as follows the mode of operation of the sewing machine will be explained with reference to the formation of a type of stitch group referred to as bar seam the bar seam illustrated in fig5 comprises a series of straight tension stitches sp which toward the end of the bar seam gradually change over to zig zag stitches the stitch length of the tension stitches sp is designated l sp at the end of the tension stitch seam lie one or more stitches designated as transverse stitches qs of zero stitch length then follows a number of zig zag stitches zz of stitch length l zz.