Samples of daophot/addstar experiments for three different fields in our study. The completeness fraction f is plotted vs. V or I magnitude in each panel. The measured f-values per 0.25-mag bin are shown as the black (I) or red (V) points with error bars. The solid lines (black for I, red for V) show the smooth fitted curves of the form f = 1/(1 + e^{α(m − m₀)}) described in the text.