The model above shows some general features of a knife edge with high cutting ability: 20° edge angle and an edge width of 1 micron for high sharpness. The edge then wears or chips down to lose sharpness through loss in height (h) and growing width (b) until it reaches approximately 10 microns which Roman calls a dull edge. The edge can dull by chipping due to lateral forces on the edge that occur during cutting: