are available at the central computer which for example can lead to a control mechanism 45 for the draw off rollers 11 or a control mechanism 46 for the spinning rotors 6 the control mechanisms 45 and 46 being formed for example by a frequency converter a display 47 at the central computer also shows the selected spinning means which as already mentioned have a not inconsiderable influence on the configuration of the effects fig4 shows a view of the fancy yarn as a placing side by side of measured values the effects 48 and webs 49 can be recognized but the beginning and end of the effects 48 and the effect thickness or the effect diameter d e and the web thickness or the web diameter d st cannot be seen clearly and therefore not adequately the sensor 12 continuously measures the yarn diameter d and transmits the measured data for evaluation via the central computer 22 to the yarn design unit 32 the yarn diameter d is recorded in each case after 2 mm of yarn length a cycle represents a measuring length of 2 mm of yarn in the view of fig5 the limit diameter d is shown as a percentage over the yarn length ls as a curve 10 the curve 50 represents the web diameter d st in the view of fig5 beginning from the left up to the point 51 from the point 51 the curve 50 rises and passes the value of the limit diameter d gr at the point 52 at point 53.