Not everyone wants to invest the time to learn basic statistics and the meaning of SD, and that is ok. When you have a set of numbers, ES is calculated from only two of them: the maximum - minimum. On the other hand, SD is calculated using all of the numbers. Thus the SD is a more "robust" parameter and it is therefore more useful and powerful, which is of course the purpose of taking these measurements. For example, how reliable is that average velocity you just obtained? Do you think if you repeat the process that you will get exactly the same average? Well the SD can be used to establish the confidence interval for that average, then you can decide if that range is "tight enough" for your application. This question arises at an interesting time, as the Daily Bulletin has an article comparing the accuracy of the 308 to the 30-06; I doubt the conclusions comparing 99.5% to 99.2% average accuracy are valid if the SD of that data were used for a statistical comparison, meaning there is probably no difference in performance. So what? As shooters we are always seeking to achieve more consistency, higher accuracy, etc and therefore we are always comparing one case to another to decide which is better; and it is easy to draw an erroneous conclusion, especially when the differences are slight, if statistics such as SD are not used to assist in the decision process.