Cumulative size distribution approximated by a power law, N(> D)=N₀D^α, where the α-value is the slope of a straight line in the log₁₀N – log₁₀D space. Here we show the actual slope, α_act, and its standard error (grey area), of a synthetic Athor family resulting from the dynamical and collisional evolution of an initial distribution of family members with slope α_ini for 3 Gyr. The horizontal dashed line denotes the actual observed slope of the real Athor family (-1.67). The two curves cross at α_ini=-2.37, which indicates the initial slope of the cumulative size distribution of the family.