This application computes the ARL (Average Run Length) of a Xbar control with variable sample size (VSS). In addition, it performs an optimization of the parameters (warning limit, control limits and the two sample sizes) in order to minimize the out-of-control ARL. It draws the ARL curves to compare the performance of the standard Xbar chart and the Xbar with VSS. There is a twin application for iOS / iPhone available in its store. At the moment the supported languages are Spanish and English.