The grind of a blade refers to the shape of the cross-section of the blade. It is distinct from the blade profile (e.g., clip point or drop point knife, sabre or cutlass, axe or chisel, etc.), though different tools and blades may have lent their name to a particular grind. Grinding involves removing significant portions of metal from the blade and is thus distinct from honing and polishing. It is notably done when first sharpening the blade or when a blade has been significantly damaged or abused (such as breaking a tip, chipping, or extensive corrosion) A well maintained blade will need less frequent grinding than one which is not treated well. The terms edge angle and included angle can be important when talking about grinding. The edge angle is measured between the surface of an edge and a line running from the point of the cutting edge to the centre of the back edge. The included angle is the sum of the edge angles. All other things being equal, the smaller the included angle the sharper the blade and the easier it is to damage the edge. An appropriate grind will depend upon what the blade is to be used for and the material from which the blade is made. Knife manufacturers may offer the same model of knife with different grinds on the blade and owners of a blade may choose to reshape it as a different grind to obtain different blade properties. A trade off exists between a blade’s ability to take an edge and its ability to keep an edge. Various grinds are easier to maintain than others or can provide a better shape over the life of the blade as the blade is worn away by repeated sharpening. In material science terms, harder steels take sharper edges, but are more brittle and hence chip more easily, while softer steels are tougher, and are used for knives such as cleavers which must be tough but do not require a sharp edge. In the range of hardnesses used for knives, the relationship between hardness and toughness is fairly complex and high hardness and high toughness are often possible at the same time. As a rough guide, Western kitchen knives generally have a double-bevel (approximately 15° on the first bevel and 20–22° on the second), while East Asian kitchen knives are made of harder steel and are ground at 15–18°, being either wedge-shaped (double-ground) or chisel-shaped (single-ground).