@windlove what do you mean by "if there are particle sizes has...

@windlove what do you mean by "if there are particle sizes has density near 0 all the way up to 1000, the researcher should investigate those to make sure they are just measurement errors, and shouldn't even present them in the plot like this" it's not 'density' its volume fraction of particle size. What the measurement error associated with 0%? I'm thinking the semi-log scale used here is confusing you, as evidenced by your comment about the peak being in the middle of the graph and that because the scale goes from 0-1000 and because its bell shaped average must be 500, which I've shown you is wrong, and I note you wont own that mistake. 1808u1 would not be left skewed if they omitted the 0 values after about 105 micron where it approximately hits 0. The curve would be bell shaped between 0-105 with a max at 45, and note that the left "tail" is from 0-10 and the right tail would be from 100-105. However the skewness and especially the kurtosis of this curve is difficult to judge due to the semi-log nature of the of the graph.