adaptor 6 in adapter 6 the value adaption to the fiber material being used occurs in adapter 6 the characteristics of the fiber material are taken into account such as fuzziness and compressibility this is done by means of a multiplication factor that correspondingly reinforces or weakens the respective value thus the fiber band dependent influences i e factors can be determined by an empirical method of operation and input into adapter 6 as pre specified data in this way the inverse function is so brought into a coordinate system that it lies precisely on the speed dependent error curve in a further development of the invention adapter 6 can be manually activated that is in accord with the type of the fiber the adaption can be altered by the operating personnel this so adjusted correction value now leaves the adapter 6 and exits apparatus 3 whereupon it is sent into correction apparatus 1 the correction of each original measurement value by this incoming corrected value is accomplished in correction apparatus 1 thus regulator control 2 contains the now fully corrected measurement value in order to check the correction value produced by the correction procedure that is the position of the pertinent inverse function a settings control is necessary a possibility for making this check is found in observing the resulting correction.