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
The average roughness (or “Ra”) value of a surface is the most common number describing the “amount” of roughness on that surface. While the Ra value (or “Sa” for areal / 3D measurements) may give a general sense of the surface texture, it cannot distinguish between two surfaces of different shapes. For example, a jagged surface with sharp spikes could have the same Ra value as a smoothly plateaued surface with lots of deep porosity. As we show in this video, describing a surface using only Ra is like describing a concert only by loudness! Yet, Ra (or Sa) may still have its uses in some production settings.
