Histograms for glucan, xylan, lignin, and ash of the 232 sample calibration set. Composition was measured on a percent dry weight basis. Frequency refers to the number of samples with a given weight percent for each constituent. The blue lines represent normal distributions and are intended to highlight any discrepancy between the histogram and normality. The calibration set does not have normal distribution for any of the constituents, which is not unexpected for a multispecies feedstock population.