Universal inherent fluctuation in statistical measurement of large particle concentration. Each set of colored dots represents the error defined by Eq. (1), half width of 95% confidence interval divided by the mean, which is obtained from the dataset with the same color shown in Fig. 2. The blue solid curve indicates inherent error, as given in Eq. (3). The dashed blue curves denote the upper and lower bounds of the error, as given in Eqs. (4,5), respectively. The blue empty circles show a Monte Carlo simulation result (see the text for details, section III). The experimental parameters, \(\alpha \)=60, \(\beta \)=15, and n=3, were used for plotting Eqs. (3) and (4,5). The inset shows the same data plots in log scale on the x-axis.