such as asperity 34 increases without the benefit of the multiple spaced apart mr sensors of the present invention the presence of asperity 34 might go undetected the present invention can also be implemented in different configurations to accommodate for different disc drive configurations for example in an embodiment in which defects are mapped using a rotary actuator to move the head a skew angle is introduced between the head and the track on disc surface thus grooves 20 can be implemented on head 10 at an angle to accommodate for the skew fig8 illustrates grooves 20 implemented on the rails of head 10 in such a manner as to offset or accommodate for the skew angle further in some embodiments other configurations or grooves 20 may provide more useful time or frequency signatures than those previously illustrated for example fig9 illustrates an embodiment in which grooves 20 do not extend all the way across the rails fig1 illustrates an embodiment in which the spacing between grooves 20 is non uniform it should also be noted that other non uniformity such as graduated spacing can also be used further fig1 only illustrates one rail in some embodiments grooves 20 and sensors 18 may be placed only on a single rail fig1 illustrates an embodiment in which the width w of grooves 20 is non uniform finally fig1 illustrates an embodiment in which grooves 20 are curved other groove configurations can also be used in other preferred embodiments in addition it should be noted that the present invention can be implemented on different types of sliders such.