Coefficient of curvature means the coefficient of curvature of the gradation of the gradation curve. Sometimes the symbol coefficient of gradation)  is used instead of formula  for  determining D₃₀ is the grain size, in millimeters, indicated by the gradation curve at the 30-percent passing level. In figure16-4,  it is (for FT-P1-1) about 0.35. Therefore,0.35² divided by (0.11 x 1.25), or about 0.89.FT-P1-1 is obviously a sand, since more than halfof its coarse fraction passes the No. 4 sieve. It is a cleansand, since less than 5 percent of it (see table AV-1,appendix V) passes the No. 200 sieve. However, it is nota well-graded sand (SW), because although itsgreater than 6 (prescribed for SW in appendix V), itsis  less  than  1,  the  minimum  prescribed  for  SW.