Keeping millstones in working order was perhaps the greatest skill in milling. Although good millstones can last for centuries, constant grinding wears them smooth. Dressing the millstone meant chiseling the furrows and removing glazed, rough, and uneven spots. The grooves carved in the grinding surface, called furrows, distributed and cut the grain, preparing it for the grinding action that occurred on the flat places known as lands. Millstones were dressed by hand with special picks, each steady stroke removing a tiny chip from the stone. The tedious work could take several days depending on the size and condition of the stones. Dressing patterns were carved in a precise and methodical way, and preferred patterns were passed down from one generation of millers to another amid much discussion and argument over which was best.