The key to preparing a defect free surface is to develop a sanding schedule that will quickly eliminate defects and leave the surface smooth enough so that tiny scratches produced by sanding cannot be seen when the wood is finished. A sanding schedule usually begins with sandpaper that is coarse enough to remove larger defects (typically 80 or 100 grit, but sometimes higher if the surface is already quite smooth), and progresses through a series of sandpaper grades that gradually remove the sanding scratches created by the previous sanding steps. A typical sanding schedule prior to wood finishing might involve sanding wood along the grain with the following grades of sandpaper, 80, 100, 120, 150 and finishing with 180 and sometimes 220 grit. The precise sanding schedule is a matter of trial and error because the appearance of a sanded surface depends on the wood you are sanding and the finish that will subsequently be applied to the wood. According to Nagyszalanczy, coarse grained woods with large pores such as oak hide sanding scratches better than fine grained wood and hence with such species it may be possible to use 180 or even 150 grit sandpaper as the final step in the sanding schedule. Conversely, sanding scratches are more easily seen in finer grained, harder woods and also end-grain, and hence, they require finer sandpaper (220 grit) during the final sanding stage. The sandpaper selected for the final sanding stage affects the colour of stained wood, and therefore when staining is part of finishing avoid sanding the wood to a very smooth finish. On the other hand, according to Nagyszalanczy if you are using an oil-based finish, it is desirable to sand the wood using higher grit sandpaper (400 grit) because oil tends to highlight sanding scratches.