Evolution of m = e² as a function of time for a range of initial starting eccentricities m₀ for R (top plot), R_π/4 (middle plot) and R^* (bottom plot). In the case of R the point of divergence between grains whose eccentricity increases or decreases with time occurs at the value of m₀ where R = 1. In the case R_π/4 the eccentricity of the grains decreases with time for all initial eccentricities; in the case, R^* the eccentricity of grains increases with time towards a maximum value for all initial eccentricities.