A logarithmic transformation of the Wentworth grade scale in which the negative logarithm to the base 2 of the particle diameter (in millimeters) is substituted for the diameter value (Krumbein, 1934); it has integers for the class limits, increasing from -5 for 32 mm to +10 for 1/1,024 mm. The scale was developed specif. as a statistical device to permit the direct application of conventional statistical practices to sedimentary data.