The sphericity scale is a measure used by geologists and geographers which measures the sphericity of a stone or particle. A geographer can determine from a stone's sphericity whether or not significant erosion has taken place in its location (such as a river). The more the stone resembles a sphere, the more erosion it has probably witnessed. This scale should not be confused with the scale which measures the shape of the stone and how angular it is.
References
Sphericity scale Wikipedia(Text) CC BY-SA