8 which can form part of the usual textile machine control components or be a unit separate and independent from this latter the unit 8 is connected to a display 10 which can also form part of said components or be totally separate from it the carriage 3 moves arrow w of fig3 along a working path or stroke comprising in known manner two phases the first phase is that of movement away from the feed member 5 while the second is that of movement towards this latter because of these phases within which the carriage moves above the needle bed 1 the feed velocity of the yarn f under constant tension has different values as can be seen from fig1 in this respect while the carriage 3 moves away from the feed member the feed velocity is whereas while the carriage 3 moves towards the feed member 5 the feed velocity is these different velocities are indicated by v 1 and v 2 in the graph of fig1 by monitoring the feed velocity or any other quantity related thereto for example by monitoring the feed member motor torque its regulation or the actual measured ayl etc automatic synchronization can be achieved between the ayl and the two movement phases of the carriage 3 the method of the invention will now be described with reference to fig2 the device.