by a short thinner extent before the steep rise 35 of the yarn diameter d f to the diameter of the test piecing 33 a check 314 to determine whether the total number n ag of the stored test piecings is equal to the preset number n at of test piecings is performed thereafter if the check 314 shows that n ag does not equals n at a move 306 to the next spinning station takes place if the check 314 shows that n ag equals n at the averaging 315 of all stored test piecing profiles is performed fig4 is another graph which shows a piecing profile averaged in this way in comparison with the graph in fig3 the path of the graph in fig4 is smoothed to a large degree and is therefore more easily accessible for evaluation the thinner extent 36 in the averaged piecing profile downstream of the piecing 37 is distinctly visible in fig4 the measuring at 316 of the thinner extent 36 in the averaged piecing profile takes place thereafter it is necessary in the course of measuring the thinner extent 36 at 316 to take into consideration that the standard yarn thickness d fn is based on an upper yarn end which has been created without the reduced draft v red as the standard therefore the end 38 of the thinner extent 36 is distinguished by arriving at a comparison diameter d v which is greater than the standard yarn thickness d fn the comparison diameter d v is a result of the equation f fm is a factor which is determined from the standard draft v nenn which obtains during normal spinning operation and the reduced draft v red and is determined as follows f fn.