insertion cycles run output signal 11 does not show instabilities 13 within range x both sensitivity levels are lowered by one step it then is observed over the next consecutive number nmin whether instabilities 13 occur if not both sensitivities again are lowered by one step this is continued until instabilities 13 occur during observation in range x if yes both sensitivity levels immediately are raised by one step then again it is observed whether for nmin consecutive insertion cycles instabilities 13 will occur if no instabilities occur again both sensitivity levels are lowered by one step and so on said method is carried on during the operation of the weaving machine m such that the effectively used working sensitivity level hi always will oscillate around an optimum sensitivity level the end point or angle of the observation range x has to be the same angular position at which the weaving machine control unit c stops to consider the output of weft yarn feelers to generate a weaving machine stop signal said end position furthermore is related to the position where the receiver rapier 3 releases the weft yarn y the weft feeler s with its control circuit is using two different sensitivity levels namely the higher working sensitivity level hi and the lower observation sensitivity level lo both preferably differing by one step only however it is possible to use other bigger and smaller differences as well said observation can be carried out for one weft feeler s only and can be used to adjust the sensitivity levels of other.