Error polygons and error bars are commonly used graphical methods for showing the precision associated with means on triangular diagrams and orthogonal plots, respectively. If the error or precision associated with a mean, based either upon counts of individual components or upon count ratios, is to be defined using basic statistics, the confidence interval method should be used. Standard deviation alone, which has been frequently in the literature, is not an appropriate statistic to use for this purpose. The graphical use of confidence intervals permits a rapid visualization of statistically significant differences between means, and thus more quantitative description of detrital clastic composition. Previous investigators using the standard deviation method have underestimated the precision of their data when sample sizes are large, and overestimated precision with small samples.