This graphic shows a horizontal series of blocks. The first 6 blocks are gray. The right edge of the last gray block is labeled "Low HWM." The next 2 are empty, followed by one gray block, and then followed by 1 empty block. The right edge of the empty block is labeled "Low HWM." The next 4 blocks are empty. The legend indicates that an empty block is "Never Used, Unformatted." A gray block is "Used." An arrow goes left to right, touching down on each used block, and then stopping at the high water mark.