A tape drive may calculate a slope for each of the timing-based-servo marks in a timing-based-servo group. The timing-based-servo marks are arranged in one or more M-patterns. The tape drive may average the slope for each of the timing-based-servo marks across the one or more M-patterns. The tape drive may generate a least-squares assessment of the averaged slope. The tape drive may determine, from the least-squares assessment, whether the averaged slope is demonstrative of tape-creep.