16 into resilient contact again with the stop 23 for the contrary rotation of the pinion 15 during the next reversal of movement of the carriage and consequently to produce the balance in relation to the other retractor element 20 with each reversal of movement of the carriage the retractor elements 20 21 and the switch finger 11 pass through the basic position as it is shown in fig2 and 3 the position sensor 13 is connected to an electronic circuit which monitors the basic position of the retractor elements 20 and 21 each time that the stepping motor 1 passes through the zero position and in the event of any deviation from the basic position due to a possible shifting of the stepping motor 1 switches off the knitting machine to summarise briefly therefore with the tension adjusting device of the present invention the retractor elements 20 and 21 both for the leftward and rightward travel of the carriage are connected to a single stepping motor 1 the retractor element which is the leading element at any given time no longer needs to be mechanically mounted for pendular movement but with the adoption by the trailing retractor element of the retracted position moves automatically into the level cams position while the racks 16 and 17 are always displaced through the same distance the position taken up by the stepping motor 1 is held by compression springs 4 of the electromagnetic brake 3 which itself is without current during the knitting process and is only energised with current for so long as the stepping motor 1 is functioning the passage of the stepping motor 1 through the zero.