Plainsawing is perhaps the most straightforward way to cut rectangular-profiled boards out of a round log. Sawmills create plainsawn lumber by cutting a log lengthwise with a series of parallel cuts. This system provides excellent yield because it minimizes scrap, but plainsawn lumber has some disadvantages. Depending on where they were cut out of the log, plainsawn boards can have substantially different grain patterns, which can cause it to expand and contract in different ways. Plainsawn wood, however, often has interesting grain patterns, sometimes called cathedrals, that are not created by other types of cutting.