In {TAIL ~ case} a gap between a bisecting line BL12 which bisects the pinhole SS12 along the longitudinal direction of the focused tracks and the center line CL11 is identical to that between a bisecting line BL13 which bisects {HEAD ~ the pinhole SS13} and the center line CL11 along the longitudinal direction of the focused tracks, the first portion of the focused laser beam containing the data read from the target track entirely passes through the pinhole SS11 
In { TAIL ~ case } a gap between a bisecting line BL12 which bisects the pinhole SS12 along the longitudinal direction of the focused tracks and the center line CL11 is identical to that between a bisecting line BL13 which bisects { HEAD ~ the pinhole SS13 } and the center line CL11 along the longitudinal direction of the focused tracks , the first portion of the focused laser beam containing the data read from the target track entirely passes through the pinhole SS11
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