reading element 21 is suitable for transmitting a magnetic excitation signal to the wearing element 20 and for capturing a magnetic signal from the wearing element 20 as a response to the magnetic excitation signal as the wearing element 20 wears the magnetic response signal to be received by the reading element 21 varies such that by means of detecting determining the variation the wear of the wearing element 20 and therefore of the blade 10 can be determined as will be discussed in more detail below according to some implementations the magnetic response signal comprises a specific frequency varying with the wear of the wearing element 20 such that the frequency of the signal is representative of the wear or of the level of wear of the wearing element 20 and therefore of the wear of the blade 10 the arrangement of the wearing element 20 in the blade 10 with respect to the end 10 a of the blade 10 depends on the degree of wear to be measured for example the wearing element 20 can be arranged such that it is flush with the end 10 a of the blade 10 such that the wearing element 20 contacts the roller and starts to wear from the time in which the blade 10 wears the change in the frequency of the magnetic response signal is therefore directly proportional to the wear of the blade 10 the wearing element.