u00b0 n each the particular advantage of this arrangement of sensors is in sensing short wavelength bars that may be associated with cover wear as each sensing element is at a different rotational position fig9 a and 9b show three continuous lines 24 28 and 32 of sensors 26 30 and 34 which extend around the sensing roll in a partial revolution a 120 u00b0 revolution in this manner only a partial helix is formed around the sensing roll 10 by each set 24 28 and 32 this arrangement of sensors 26 30 and 34 allows group of sensors to be assigned to a particular cd position like the sensing roll 10 shown in fig6 a and 6b adjacent sets 24 28 and 32 are spaced 120 u00b0 circumferential apart from each other along the roll see fig9 b fig1 a and 10b show four continuous lines 24 28 32 and 36 of sensors 26 30 34 and 38 which extend around the sensing roll in a partial revolution a 90 u00b0 revolution again only a partial helix is formed around the sensing roll 10 by each set 24 28 32 and 36 this arrangement of sensors 26 30 34 and 38 allows group of sensors to be.